OIS 3660- Final Study Guide (Pt.1)

The stages of a certain manufacturing process have the following capacities: Stage 1: Capacity = 20 per hour per processor, one processor Stage 2: Capacity = 12 per hour per processor, two processors Stage 3: Capacity = 1 unit per 6 minutes per processor, three processors Which of the three stages is the bottleneck of the process?

Stage 1

At an airport, Delta needs to check in two flights that leave at the same time. For each of the two flights, 160 passengers will arrive randomly over the next two hours. There are 3 employees assigned to each flight and each employee can help a passenger on average in 2 minutes (due to online and kiosk check-ins - this used to be 10 minutes), with a standard deviation of 2 minutes. How much does the average waiting time decrease when these two flights are pooled such that all passengers can go to all six employees? (First solve for the wait time assuming two "unpooled" systems, each of which has an arrival rate of 80 per hour. Then solve for the wait time assuming a pooled system, with m=6. Then find the difference in wait time.)

Approximately 2.67 minutes

A local bank branch employs three tellers who can each help a customer on average in 6 minutes, with a standard deviation of 3 minutes. On average, 24 customers arrive at this bank per hour (in a random fashion). How long would customers have to wait if we pool the employees?

Approximately 4.16 minutes

A lower throughput time can be achieved with smaller batches, but this would lead to higher utilization. Which of the following would allow us to use smaller batch sizes (i.e., more batches)?

Lower setup time, lower variability

A process consists of two subsequent stages, each with their own setup times per batch, and pure processing times per unit. Each stage has one processors, and the other input is as follows: Stage 1: setup time per batch = 3 minutes, pure processing time per unit = 2 minutes Stage 2: setup time per batch = 5 minutes, pure processing time per unit = 1 minutes An order of 60 units comes in when the system is completely empty (i.e., not working on anything). This order is split into three batches of 20 units each. After how much time are ALL units completely done?

154 minutes

At a Mexican fast-food chain, a customer a) decides what type of food s/he wants (e.g., burrito, salad, or tacos), b) decides what fillings s/he wants (e.g., chicken, fish, or vegetable), c) decides what toppings s/he wants (e.g., lettuce, guacamole, or cheese), and d) pays for the order that may or may not include a drink. One employee works at each of the steps a) through c), and two employees take care of the payment. Per customer, step a) takes 2 minutes on average, step b) takes 3 minutes on average, step c) takes 1 minute on average, and step d) takes 4 minutes on average. By how much would the system capacity increase if another person is hired for step b)?

50%

Emergency rooms (ERs) at hospitals cannot make appointments with clients since you never know who needs emergency care when (or even what kind of emergency care the patient needs). On the other hand, dentists can make appointments. Let's assume that both healthcare providers (ER and dentist) receive the same number of patients in a day and that they are able to help a patient in the same time, so the only difference is that the dentist can schedule his/her patients, and the ER cannot. Where would the queue, on average, be longer?

At the ER due to the curse of variability

The School's maintenance department has 4 painters. If one painter goes to an office to do the painting, it takes her 10 minutes to get set up to paint, followed by 10 minutes to paint each wall (50 minutes total to paint all 4 walls). Due to the disruption caused by a painter, each office must be vacated for the full time it is being painted (but no other office need be vacated). If all 4 employees go, then it takes each employee the same 10 minute setup but the 4 walls then take only another 10 minutes to be painted simultaneously (the office must be vacated for only 20 minutes). While the School wants to vacate each person's office for the shortest time possible, it must get 4 offices painted per hour on average. What should the batch size be for the walls in an office?

Batch size of 2 (2 wails should be painted by one painter)

By how much, on average, would the time spent in the system decrease if three servers were pooled in the following setting (note: all answers are rounded to whole minutes): 1) Three servers each with their own queue. 2) Arrival rate of 15 customers per hour, arriving randomly and picking one of the three lines randomly. 3) Processing time of 10 minutes per customer, with a standard deviation of 5 minutes.

Before pooling: 41 minutes, after pooling: 19 minutes, so a decrease of 22 minutes

Let's say that we are in a system with 10 un-pooled servers and a variability factor of 1 and we currently have an average inventory in the queue of 4 since we have a utilization of 80%. If we want to cut the average inventory in the queue in half, then what should we do?

Create five sets of 2 pooled servers If we were to do this, then we pool 2 servers (five times) so we move from the blue line with a "1" on it to the pink line with a "2" on it. Since pooling does nothing to the utilization, we simply move straight down from the 4 on the y-axis to the 2 on the y-axis, effectively having cut the average inventory in half!

Which of the following products is most likely processed in a flow shop?

Crude oil

A production facility faces a rather stable demand and has a fixed capacity, which is based on the number of IGN-99 machines. The average demand is 100 units per week, and each of the four IGN-99 machines can deliver 99 units per week (hence the name). These IGN-99 machines are rather expensive to operate. Which statement is most correct?

Given the current low utilization, they should sell (or at least not run) two of these IGN-99 machines.

There is a system with subsequent stages which just received an order for many units that it can split into smaller batches if it wants. At each stage there are very high setup times - what does this (qualitatively) mean for the best batch size?

Go for larger batch sizes to reduce the utilization

Where can we find the R from Little's Law (I = RT) when applying it to a Cash Flow Cycle problem?

In the income statement

A popular ride at Six Flags has two carts that each take exactly 5 minutes for a round (i.e., thrill seekers get in, ride does its thing, thrill seekers get out) and can take 40 thrill seekers each (assume that it is always full). You can assume that each seat in a cart is a "server", or m = 80. Per hour, on average 950 thrill seekers are attracted to this popular ride, who arrive at completely random times. How many thrill seekers are waiting for this popular ride on average?

Approximately 42

How many different types of machines are there in the Littlefield Simulation (not "number" of machines, but number of types of machines - this question is effectively asking how many "stations" there are in the game )?

3

Assume Shouldice has 90 beds and each patient stays exactly 3 nights. Further assume Shouldice admits patients five consecutive days per week, and admits the same number on each of these 5 days. At most, how many can they admit per each of these 5 days?

30

A party of 5 goes to the Green Iguana. The waiter takes 10 seconds to get from the kitchen to the table (or vice versa), and takes 30 seconds to manually take each person's order at the table. The waiter always starts in the kitchen, goes out to a table, takes the order, and then delivers the order to kitchen. If the waiter takes the table's orders in a batch of 5, what is the "pure process time"?

30 seconds

Why should the batch size be larger at a bottleneck than at a non-bottleneck?

Because the bottleneck's utilization is limiting the system's utilization

So we know where a Fire Station should locate itself on the OM Triangle, but how about eBay?

Close to the Information corner

When comparing two companies, we notice that they are very similar in setup (e.g., same costs, same profit margins, same inventory turnovers etc.). However, the time it takes company A to pay for raw materials is longer than it takes company B, while the time it takes customers of company A to pay for the finished goods is shorter than it takes company B's customers. Which of these companies has a shorter cash flow cycle?

Company A

At the core, what is Operations Management about?

Processing inputs into outputs

If a process step has a LARGE setup time and a SMALL pure-processing time per unit, what batch size will result in the fastest throughput time for any ONE unit through this step? Assume there are multiple resources at this step, each with plenty of capacity.

Small batch size

Apple's sales in the first quarter of 2016 were $60 billion Apple's accounts receivable were approximately $12 billion How many days does an entry remain in accounts receivable? Assume 90 days in the first quarter of 2016.

T = 18 days

What do the green triangles represent?

The WIP (Work In Process) inventory prior to each process step

Little's Law describes:

The average performance of a system in terms of Inventory, Rate, and Time.

If we can somehow REDUCE the variability, what would happen to the optimal batch size (i.e., in terms of throughput time)? Assume that everything else (e.g., processing time, setup time, etc.) stays the same, so ONLY the variability is reduced.

The batch size would also decrease

In the figure below, what happens if the cost of capacity goes down? Assume variability remains unchanged.

The optimal "x-value" goes down and the optimal "y-value" goes down.

How are the concepts of utilization and a bottleneck linked?

The process step with the highest utilization is the bottleneck in the system

What do the circles represent?

The process steps

If a company has a negative cash conversion cycle, then this indicates that:

This company gets paid for the purchased goods before it pays for the delivered goods.

When Ford started creating cars, he introduced the assembly line such that each employee only had to take care of a specific job. Cars left the manufacturing plant one-by-one at fixed time intervals. What type of facility does this describe?

Line Flow

In a system without any variability and a utilization of 99% we pool three queues into one queue. What is the result?

Waiting times stay the same and utilization remains the same as well

Imagine a simple process in which 5 ticket booths are selling tickets for an opera. If customers are coming at a rate of 15 / hour, and the utilization of the 5 booths is 50%, then how long does a customer spend at a booth (each customer goes to only one booth)?

10 minutes

At a supermarket 200 customers arrive per hour (and 200 depart per hour, but not necessarily in the same hour they arrive). Each customer spends on average 30 minutes in the supermarket. What is the average number of customers in the supermarket?

100

A used cars lot has 100 cars in inventory on average. They sell 25 cars per week on average. How many times is inventory turned over per year at this used cars lot (assume a year has 52 weeks)?

13 times

Continuing with the previous homework problem, what is the minimum amount of time the student needs to study each night?

130 minutes

What would be the throughout time for an order of 60 units in the following system (draw it!!): Two stages in sequence (n = 2) One processor at each stage (m = 1) Processing time 2 minutes per unit at both stages (p = 2 minutes) No setup time Work in a batch size of 20 (so b = 3, because there are 3 batches of 20 units each)

160 minutes

In a popular vacation destination in Asia, all of the hotel beds are generally booked in the summer season. On average, there are 2,800 tourists who stay, on average, for two weeks (i.e., 14 days). How many new tourists arrive, on average, per day in this vacation destination?

200

Working on a batch has a setup time of 5 minutes and a pure processing time of 2 minutes per unit. A particular resource has two processors. If an order comes in of 12 units, which is split into four batches of three units (i.e., each processor works on two batches of three units), then what is the total throughput time for this order at this resource? Assume there is no wait time.

22 minutes

A party of 5 goes to the Green Iguana. The waiter takes 10 seconds to get from the kitchen to the table (or vice versa), and takes 30 seconds to manually take each person's order at the table. The waiter always starts in the kitchen, goes out to a table, takes the order for the batch (whatever the batch size), and then delivers the order for only that batch back to kitchen. If the waiter takes the table's orders in batches of 1 (only taking the order of 1 person), what is the waiter's total time required to process the job for the entire table?

250 seconds

If you want to produce a standard product in extremely large quantities, then you should work according to a:

Flow shop

Let's say that you are currently operating close to the inventory corner on the OM Triangle and you want to get away from there. What could you do?

Invest in more Capacity

Qualitatively, what does pooling (when talking about queues) mean?

It means that the servers are "pooled" together, such that there is only a single queue

select the answer that best describes which area requires the most skilled labor? Someone working in a...

Job Shop

What is Big Medicine?

Larger chains of hospitals that offer low cost high quality care

Let's say that your process is currently positioned somewhere on the triangle (doesn't matter exactly where), and you have just received a great deal on new machines which are much cheaper than the ones you are currently using (and are in need of replacement). If you were to re-position your process on the triangle accordingly, then in which direction would you move?

Left (perhaps down a bit as well)

Which of the following requires the least skilled and most repetitive labor?

Line flow

Meal service to the economy class on an airplane should be located where in the OM Triangle?

Low Capacity, medium Inventory, and medium Information

Continuing with the earlier "homework" question, the student proposes to break each professor's daily assignment of 10 problems into 10 lots (the previous problem assumed 2 lots of 5, now the proposal is 10 lots of 1, meaning an op's problem followed by an accounting problem followed by an op's problem...). What will be the student's implied utilization?

More than 100%

An assembly line:

Most closely resembles line flow

Focusing on the beginner's sets - how are these produced?

Most closely resembling a batch flow

A company that produced drum sets makes three types: a beginner's set for $150, an intermediate set with some customization options for $499-$599, and a high-end fully customizable set for $1000-$1500 (depending on the customization). This company employs three types of employees: top technicians who have been with the company from the start, journeymen who have been with the company for 2-5 years, and newbies who have been with the company for 0-2 years. They receive orders for the high-end drum sets randomly throughout the month, and they put their top technicians to work on those to ensure a high quality and fast delivery. The intermediate sets are basically a standard kit plus three options (i.e., customers can choose these out of a set of seven options) for which they receive approximately ten orders every week. The standard kit of this intermediate set is put together by their newbies who are working on these continuously, while the options are completed by their journeymen. Finally, the beginner's sets are put together by whatever time the top technician or the journeymen have left over (i.e., the newvies are continuously working on the standard kits of the intermediate sets). That is, if a top technician or a journeyman has completed his/her job and there is nothing waiting, they work on the beginner's set. To limit the setup time, once they start on an item for the beginner's set, s/he makes a batch of 5 before s/he checks to see whether a new order for a top-level (top technician) or intermediate set (journeyman) has come in. Focusing on the high-end fully customizable set - how are these produced?

Most closely resembling a job shop

Focusing on the standard kit of the intermediate sets - how are these produced?

Most closely resembling a line flow

Operations is... Only important if you are running a hospital Only important in manufacturing Only important if you want to get a degree

None of the other answers are correct

What are the inputs and outputs of FEDEX?

Packages that are not in the right location & packages that are in the right location

What is NOT a resource for an airline?

Passengers

What is the main input for an airline?

Passengers

What is the output of an airline?

Passengers at their destination

While the shoppers' opinions vary on self checkout, self checkout does mitigate the curse of variability to some extent - which is it?

Pooling multiple queues into one

The two pictures below show us what happens when we pool servers & when we decrease the variability. From these pictures we can clearly see that:

Pooling servers reduces the average inventory in a similar fashion as reducing the variability

Which of the following statements concerning Little's Law (I = RT) is correct?

R denotes the arrival rate per time unit

Which of the following restaurants most resembles a Job Shop (feel free to visit their websites)?

Valter's Osteria

How is it possible that queues occur even when the utilization is lower than 100%?

Variability causes the system to sometimes sit idle (but this time cannot be stored) and be really busy at other times (leading to queues)

Operations processes use "resources" to transform inputs into outputs. Which of these is a "resource" for a water slide park?

Water slides

In a Subway sandwich line, there are three stages in the process: Base ingredients, Toasting, and Toppings. There is one machine for each stage. What is m for the Toasting stage?

1

If demand for hula-hoops is 200 units per day, and demand for strawshooters and wingdingers is 0, then what is the (implied) utilization of Forming?

100%

An op's professor assigns her students 10 op's questions every day. After the student "prepares himself" to work on operations, each problem takes 6 minutes to work. An accounting professor similarly assigns 10 questions every day, each of which takes 6 minutes to work after the student is "prepared" to work on accounting. The student has 3 total hours available for studying every night. Unless the student just completed an op's problem, it takes the student 5 minutes to get prepared before tackling an op's problem, and similarly, unless the student just completed an accounting problem it takes the student 5 minutes to get prepared before tackling an accounting problem. What is the minimum amount of time the student needs to study each night?

130 minutes

In a small restaurant in a French village in the Alps, the food is so good that people on average wait 60 minutes before they get a table. If there are on average 25 people waiting in a separate waiting area, then how many people arrive at this restaurant per hour (on average)?

25

Consider the graph below in answering the following OM Triangle question. We are currently located at an average inventory in the queue of (almost) 7 due to a variability of 2 and a utilization of 0.8. If we want to leave this position in the Inventory corner, and we want to make our way to the Information corner, then by how much should we reduce the variability to achieve an average inventory in the queue of approximately 1.5? Assume utilization remains unchanged. As always, look at all the answers and choose the best!

Approximately 75%

By how much, on average, would the total number of customers (the sum of those in all queues plus those in all servers) change if two servers were pooled in the following setting: 1) Before pooling, there are two servers each with their own queue. 2) Each server has an arrival rate of 5 customers per hour, arriving randomly. 3) Each server has a processing time of 10 minutes per customer, with a standard deviation of 10 minutes. Remember, the question is asking about the TOTAL number of customers in all queue(s) plus those in all servers.

Before pooling: 10 customers, after pooling: 5.5 customers, so decrease of 4.5 customers

A process has a setup time of 5 minutes (every batch, or "lot" of items, incurs exactly one setup). Which batch size will result in the highest implied utilization?

Lot size of 1

The P-A-D law firm offers 3 types of consultations; pre-nups (product P), annulments (product A), and divorces (product D). P-A-D has 4 employee types that are used in processing these cases - the process times required for each product at each employee type (and the number of employees of each type) are shown in the table below. Each employee works 10 hours each day, 4 days per week. If demand is 100 per workday for pre-nups (P), 10 per workday for annulments (A), and 20 per workday for divorces, then which resource type is the bottleneck?

Partner

In a system with two subsequent stages, stage 1 has two processors, each with a capacity of 8 units per hour, and stage 2 has three processors, each with a capacity of 6 units per hour. Which of these two stages is the bottleneck?

Stage 1

Let's consider three resources: the Triage nurse, the doctors, and the hospital beds. Which of these should most logically be the bottleneck in the Emergency Room?

The doctors, as they are the most expensive resource and hardest to train

Operations processes use resources to transform "inputs" into outputs. Which of these is an "input" for a water slide park?

Thrill seekers

Consider the graph below in answering the following OM Triangle question. We are currently located at an average inventory in the queue of (almost) 7 due to a variability of 2 and a utilization of 0.8. If we want to leave this position in the Inventory corner, and we want to make our way to the Information corner, then by how much should we reduce the variability to achieve an average inventory in the queue of approximately 1? Assume utilization remains unchanged. As always, look at all the answers and choose the best!

To a variability factor of approximately 0.25.

A pharmacy has two types of customers: those who are there to pick up a repeat prescription (this takes on average 1 minute), and those who are there to pick up a first-time prescription (this takes on average 6 minutes as it requires some explanation). On average 20 customers arrive per hour who want a repeat prescription, and also 20 who want a first-time prescription. How many employees should this pharmacy hire at the bare minimum?

3

How many different kinds of products or services is this process producing/delivering?

3 There are three types of arrivals (R1, R2, and R3), so this process produces/delivers 3 kinds of products/services.

Little's Law Firm has two paralegals. Customers arrive randomly at an average rate of 10 per hour. Service times have a mean of 10 minutes and a standard deviation of 10 minutes. What is the average total time a customer spends in the system?

33 minutes

Continuing with the "homework" question, the student likes variety - it is just too boring to do too many accounting problems in a row so the student would desperately like to switch back and forth between op's and accounting as frequently as possible and yet still get both sets of problems done in 3 hours. What should the student choose as the lot size?

5 lots of 2

For a local Delta airlines flight, check-in information indicates that between 11AM and noon (i.e., 12PM), 300 passengers checked in. On average, there were 25 passengers waiting in line at the self-check-in kiosks. How long did a passenger have to wait on average before s/he could use the self-check-in kiosk?

5 minutes

A student has 3 total hours available for studying every night. An op's professor assigns her students 10 op's questions every day. After the student "prepares himself" to work on operations, each problem takes 6 minutes to complete. An accounting professor similarly assigns her students 10 questions every day, each of which takes 6 minutes to complete after the student is "prepared" to work on accounting. The student is "prepared" to immediately work on the next op's problem if he just completed an op's problem, and similarly he is "prepared" to immediately work on an accounting problem if the student just completed an accounting problem. Unless he just completed an op's problem, it takes the student 5 minutes to get prepared before tackling an op's problem, and similarly, unless he just completed an accounting problem it takes him 5 minutes to get prepared to tackle an accounting problem. What is the "pure process time" associated with completing one homework problem?

6 minutes

Continuing with the previous "homework" question, the student proposes doing the problems in batches of five, meaning completing five op's problems followed by five accounting problems followed by five op's problems, followed by five accounting problems. What will be the student's implied utilization?

7/9

Caterpillar's December 31st, 1998 balance sheet shows accounts receivable of approximately $2.5 billion, accounts payable of approximately $4.0 billion, and an inventory of approximately $3.0 billion. Their 1998 income statement shows Cost of Good Sold (COGS) of approximately $15 billion, sales of approximately $20 billion, and operating costs of approximately $18 billion. How many days, on average, does Caterpillar hold its inventory? Assume a year has 360 days.

72 days

After a careful analysis, managers at Haremon's have concluded that 20 customers per hour need to check out. If the sole cashier can check out 25 customers per hour, what is the cashier's (implied) utilization?

80%

At the start of the first video the Food Dude creates his burrito which has to stay on the heater plate for 2 minutes. In the second video (at 2:24) we see that a heater plate fits 5 burritos*. If we need 120 burritos every hour, then what is the utilization for the heater plate? Assume that the person who operates the heater plate is able to replace burritos in under a second.

80% Since each burrito must stay on the heater plate for 2 minutes (this is the processing time), the capacity for one "resource" (i.e., one spot on the heater plate) is 30 burritos per hour: (60 minutes / 1 hour) / (2 minutes / burrito) = 30 burritos / 1 hour, or 30 burritos per hour. However, since the heater plate can simultaneously heat 5 burritos (i.e., it has 5 "resources"), the total capacity of the heater plate is 5 x 30 burritos per hour = 150 burritos per hour. The demand is 120 burritos per hour, so the utilization is 120 burritos per hour /150 burritos per hour = 80%.

Given the following system with 3 resources (m = 3) and three job types (n = 3): R1 = 10/hr, R2 = 5/hr, R3 = 2/hr & c1 = 10/hr, c2 = 5/hr, c3 = 5/hr What is the utilization of this system?

80% u=R/mc 10/(10*3)=0.333 + 5/(5*3)=0.333 + 2/(5*3)=0.133= 0.80

In the video the narrator discusses the capacity of two popular rides at Universal Studios in Florida: The Incredible Hulk and Hollywood Rip Ride Rocket, which are both almost 2000 riders per hour. Let's assume that the actual number of riders per hour is 1800 (some seats remain empty) and that riders wait on average 30 minutes to get in (the video is all about minimizing these times!) - how many riders are then waiting on average?

900 riders The inventory is the number of people waiting at a ride, and the number we are trying to solve for. The arrival (or departure) rate is equal to the number of riders per hour so 1800, and the time riders wait at the ride is given as 30 minutes. Therefore: 1800 riders per hour * half an hour = 900 riders are waiting for the ride on average!

60 customers/hr arrive randomly and randomly join one of 6 unpooled queues. Each of the six employees can handle exactly 15 customer requests/hr (i.e., no variability). What percentage reduction in waiting time does pooling of all six queues into one queue offer?

92%

Wham-O makes 3 plastic toys; hula-hoops (product H), strawshooters (product S), and wingdingers (product W). Wham-O has 4 resource types that are used in production - the process times required to make each toy at each resource type (and the number of processors of each type) are shown in the table below. For example, hula-hoops must go through Extrusion, Forming and Packaging (but hula-hoops do not require any process time at the "Finishing" step). Each resource is operated 10 hours each day. For example, in one hour, Extrusion can process 40 hula-hoops if it only works on hula-hoops (i.e., one every 3 minutes, so 20 per hour, for each of the two processors), or it can process 30 strawshooters if it only works on strawshooters, or it can process 60 wingdingers if it only works on wingdingers (alternately, it can process some combination of H, S, and W). If demand is 100 units per day for hula-hoops, plus 100 units per day for strawshooters, plus 120 units per day for wingdingers, then what is the utilization of Forming?

95%

Fastfood restaurant A uses a single queue, while B uses multiple queues - where will customers experience shorter waiting times (on average) and where will customers think the waiting is more fair?

A has shorter queues and will be perceived as more fair

If a process step has a LARGE setup time and a SMALL pure-processing time per unit, what batch size will result in the fastest completion of ALL of the units at this step? Assume there is only ONE resource at this step.

A large batch

Which of the following statements about the curse of variability is correct?

A reduction in variability can lead to a reduction in inventory

If a process step has a LARGE setup time and a SMALL pure-processing time per unit, what batch size will result in the highest utilization?

A small batch

If a process step has a SMALL setup time and a LARGE pure-processing time per unit, what batch size will result in the fastest throughput time for any ONE unit through this step? Assume there are multiple resources at this step, each with plenty of capacity.

A small batch

If a process is best situated close to the information corner of the OM triangle, then this must mean: All the other answers are correct Capacity is very expensive, so we limit how much we buy, leading to high utilization There is little waiting for this process There is low variability in arrivals and processing times

All of the above

If a process is best situated close to the inventory corner of the OM triangle, then this must mean: Capacity is very expensive, so we limit how much we buy, leading to high utilization There is a lot of variability in arrivals and processing times All the other answers are correct Waiting or throughput times are long for this process

All of the above

Which of the following is an example of controlling variability in demand? Happy hour at a bar All the other answers are correct Discount movie tickets for movies in the afternoon

All of the above

Why should you study Operations Management? It tells you how to make money All the other answers are correct It tells you how to manage transformations from inputs to outputs It teaches you how to think logically

All of the above

A local bank branch employs three tellers who can each help a customer on average in 6 minutes, with a standard deviation of 3 minutes. On average, 24 customers arrive at this bank per hour (in a random fashion). How long would customers have to wait if we do NOT pool the employees? (By "not pooling," we mean we have 3 separate lines forming; one in front of each of the 3 tellers. Assume that a person randomly enters one of the lines - each of the 3 lines takes one-third of the arrivals - and a person does not switch lines after entering a line.)

Approximately 15 minutes

The Krasnapolski is a top-of-the-line hotel in Amsterdam, the Netherlands. Among their many services, they rent bicycles to guests. The bicycle checkout is open 24 hours per day 7 days per week and has 50 bicycles on hand. On average, 10 guests request a bicycle each day, arriving completely randomly at all times of the day during the spring and summer seasons. Guests keep bicycles for four days on average, with a standard deviation of two days. How long does a guest on average have to wait for a bike?

Approximately 47 minutes

In the video it states that a giant oven bakes 80,500 cookies every 12 minutes. It takes 6 seconds to fill up a tray with the dolloper machine and load it onto an oven rack (check the video), and there are 48 cookies on a single tray (6 by 8 as can be seen in the video). Let's assume that we currently do not have ANY cookies ready, but we do have a large batch of dough, plenty of helping hands to man the dolloper machine, and the oven is already at the right temperature. How many cookies can we have ready in 30 minutes? Taking them out of the oven and getting them ready to serve takes 1 minutes...

Approximately 8,000 Correct! At 6 seconds per tray, we can load 10 trays per minute, and we have 30 - 12 - 1 = 17 minutes available, so we can do 170 trays of 48 cookies each = 8160 cookies! That's only 10% of the oven's capacity!

Little's Law Firm has just one lawyer. Customers arrive randomly at an average rate of 6 per 8 hour workday. Service times have a mean of 50 minutes and a standard deviation of 20 minutes. How long does a customer spend at Little's Law Firm on average?

Approximately 98 minutes

Regarding process mapping, which of the following statements is FALSE? Arrows denote how the customers walk through the process Rectangles or circles are used to identify process steps Triangles are used to identify queues or inventory Process maps can be used for both manufacturing and services

Arrows denote how the customers walk through the process

By how much, on average, would the waiting time decrease if two servers were pooled in the following setting (note: all answers are rounded to whole minutes): 1) Two servers each with their own queue. 2) Arrival rate of 10 customers per hour, arriving randomly and picking one of the two lines randomly. 3) Processing time of 10 minutes per customer, with a standard deviation of 5 minutes.

Before pooling: 31 minutes, after pooling: 14 minutes, so decrease of 17 minutes

Let's say that your process is currently positioned somewhere on the triangle (doesn't matter exactly where), and you have just purchased a wonderful IT system with lots of data that gives you far more insights into when demand arrives and how long it takes you to satisfy this demand. If you were to re-position your process on the triangle accordingly, then in which direction would you move?

Down

If demand for hula-hoops and strawshooters is 0 units per day; and for wingdingers is 400 units per day, then which Resource is the Bottleneck?

Extrusion, Forming, and Packaging have the same output per hour, so they are all bottlenecks

What does R represent? Pick the one answer which is NOT correct! Assume that the utilization of this system is nowhere near 100%.

The number of units in the system on average

Which of the following combinations does NOT have a utilization of 50%?

The system is a Doctor's office. Capacity = 5 per minute; Demand = 600 / hour.

Hammon's is contemplating opening a little stand-alone satellite store. After a careful analysis, managers have concluded that 25 customers per hour will need to check out at the satellite store (this will be the long-run average demand at the store). They are considering hiring two cashiers, each of whom can check out a customer in 5 minutes on average. What can you say about this system?

This system will be unworkable since the implied utilization is greater than 100%. The managers at Hammon's need to do something.

Consider the graph below in answering the following OM Triangle question. We are currently located at an average inventory in the queue of 7 due to a variability factor of 2 and a utilization of 0.8. If we want to leave this position in the Inventory corner, and we want to make our way to the Capacity corner, then how many more servers do we need to get to an average inventory in the queue of approximately 0.2? Assume variability remains unchanged.

We need to quadruple the number of servers

Assume a processing system with three separate queues (one in front of each of three resources). Under which of the following conditions would pooling these three separate queues into one queue reap the HIGHEST benefit?

When utilization is relatively high to begin with (e.g., higher than 90%)

There are three resources working in sequence, each with the following processing times p1 = 16 minutes, p2 = 10 minutes, and p3 = 21 minutes. Resource 1 has two processors, resource 2 has one processor, and resource 3 has three processors. What is the capacity of this system?

c=6/hr The capacity can not exceed the slowest resource in the system. In this case, resource 2 only has one processor, p2=10 minutes, 60/10= c=6/hr.

Wilford Wonka owns a candy factory that specializes in magically delicious chocolate bars of 6 varieties. After all of the necessary ingredients have been grown and harvested, they go through a complicated process of mixing, molding, and drying, after which the chocolate bars reach the last step of packaging. On average, a machine requires 5 minutes of labor to change from packaging one variety of chocolate bar to another. If the machine is configured to process a given variety of bar, it then takes 15 seconds to package each bar, regardless of the variety. There are 8 packaging machines, and each is running 95% of the workday.

m = 8, p = 15 seconds, setup time = 5 minutes, u = 95%

How many process steps are there?

n It counts process 1, process 2, ..., process n, so there are n process steps.