Stats Exam #2

X is a normally distributed random variable with a mean of 5 and a variance of 4. The probability that x is greater than 10.52 is

.0029

A population has a mean of 80 and a standard deviation of 7. A sample of 49 observations will be taken. The probability that the mean from that sample will be larger than 82 is

.0228

A random sample of 150 people was taken from a very large population. Ninety of the people in the sample were females. The standard error of the proportion of females is

.0400

A population has a mean of 53 and a standard deviation of 21. A sample of 49 observations will be taken. The probability that the sample mean will be greater than 57.95 is

.0495

A sample of 51 observations will be taken from a process (an infinite population). The population proportion equals 0.85. The probability that the sample proportion will be between 0.9115 and 0.946 is

.0819

A population has a mean of 180 and a standard deviation of 24. A sample of 64 observations will be taken. The probability that the mean from that sample will be between 183 and 186 is

.1359

In order to estimate the average time spent on the computer terminals per student at a local university, data were collected for a sample of 81 business students over a one-week period. Assume the population standard deviation is 1.8 hours. Refer to Exhibit 8-1. The standard error of the mean is

.20

Exhibit 7-2 Four hundred registered voters were randomly selected asked whether gun laws should be changed. Three hundred said "yes," and one hundred said "no." Refer to Exhibit 7-2. The point estimate of the proportion in the population who will respond "yes" is

.75

If an interval estimate is said to be constructed at the 90% confidence level, the confidence coefficient would be

.9

X is a normally distributed random variable with a mean of 8 and a standard deviation of 4. The probability that x is between 1.48 and 15.56 is

.9190

X is a normally distributed random variable with a mean of 12 and a standard deviation of 3. The probability that x equals 19.62 is

0.000

X is a normally distributed random variable with a mean of 22 and a standard deviation of 5. The probability that x is less than 9.7 is

0.0069

The weight of items produced by a machine is normally distributed with a mean of 8 ounces and a standard deviation of 2 ounces. What is the probability that a randomly selected item will weigh between 11 and 12 ounces?

0.0440

A sample of 400 observations will be taken from a process (an infinite population). The population proportion equals 0.8. The probability that the sample proportion will be greater than 0.83 is

0.0668

The weight of items produced by a machine is normally distributed with a mean of 8 ounces and a standard deviation of 2 ounces. What is the probability that a randomly selected item will weigh more than 10 ounces?

0.1587

A random sample of 1000 people was taken. Four hundred fifty of the people in the sample favored Candidate A. The 95% confidence interval for the true proportion of people who favors Candidate A is

0.419 to 0.481

The weight of items produced by a machine is normally distributed with a mean of 8 ounces and a standard deviation of 2 ounces. What percentage of items will weigh between 6.4 and 8.9 ounces?

0.4617

A population of size 1,000 has a proportion of 0.5. Therefore, the expected value and the standard deviation of the sample proportion for samples of size 100 are

0.5 and 0.050

Given that z is a standard normal random variable, what is the value of z if the area to the right of z is 0.1401?

1.08

Given that z is a standard normal random variable, what is the value of z if the area to the right of z is 0.1112?

1.22

The following data was collected from a simple random sample from a process (an infinite population). 13 15 14 16 12 The point estimate of the population standard deviation is

1.581

A sample of 75 information system managers had an average hourly income of $40.75 with a standard deviation of $7.00. Refer to Exhibit 8-6. The value of the margin of error at 95% confidence is

1.611

In order to estimate the average time spent on the computer terminals per student at a local university, data were collected for a sample of 81 business students over a one-week period. Assume the population standard deviation is 1.8 hours. Refer to Exhibit 8-1. With a 0.95 probability, the margin of error is approximately

1.95

A sample of 75 information system managers had an average hourly income of $40.75 with a standard deviation of $7.00. Refer to Exhibit 8-6. If we want to determine a 95% confidence interval for the average hourly income, the value of "t" statistics is

1.96

The following data was collected from a simple random sample from a process (an infinite population). 13 15 14 16 12 The point estimate of the population mean is

14

Imagine we are trying to sell to a customer who demands that the mean of a random sample of 64 bulbs lasts at least 2,050 hours before they will buy. The population mean = 2,000 hours, and the population standard deviation is 100 hours. What mean length of bulb life could you be 90% confident that the sample mean will be at least that long?

1984

A random sample of 64 students at a university showed an average age of 25 years and a sample standard deviation of 2 years. The 98% confidence interval for the true average age of all students in the university is

24.4 to 25.6

The weight of items produced by a machine is normally distributed with a mean of 8 ounces and a standard deviation of 2 ounces. What percentage of items will weigh at least 11.7 ounces?

3.22%

Pep Zone sells auto parts and supplies including a popular multi-grade motor oil. It has been determined that demand during replenishment lead-time is normally distributed with a mean of 20 gallons and a standard deviation of 8 gallons. If the manager of Pep Zone wants the probability of a stockout during replenishment lead-time to be no more than .10, what should the reorder point be? (Use the Standard Normal Cumulative Probability Table. If you can not find the exactly probability on the table, check page 32 of the ppt file. Just enter the number without any units. Keep two decimal places.)

30.28

Pep Zone sells auto parts and supplies including a popular multi-grade motor oil. It has been determined that demand during replenishment lead-time is normally distributed with a mean of 20 gallons and a standard deviation of 8 gallons. If the manager of Pep Zone wants the probability of a stockout during replenishment lead-time to be no more than .025, what should the reorder point be? (Use the Standard Normal Cumulative Probability Table, just enter the number without any units. Keep two decimal places.)

35.68

Random samples of size 17 are taken from a population that has 200 elements, a mean of 36, and a standard deviation of 8. Refer to Exhibit 7-5. The mean and the standard deviation of the sampling distribution of the sample means are

36 and 1.86

A sample of 75 information system managers had an average hourly income of $40.75 with a standard deviation of $7.00. Refer to Exhibit 8-6. The 95% confidence interval for the average hourly wage of all information system managers is

39.14 to 42.36

"DRUGS R US" is a large manufacturer of various kinds of liquid vitamins. The quality control department has noted that the bottles of vitamins marked 6 ounces vary in content with a standard deviation of 0.3 ounces. Assume the contents of the bottles are normally distributed. Ninety-five percent of the bottles will contain at least how many ounces? (Use the Standard Normal Cumulative Probability Table. Check page 32 on ppt file for an example. Just enter the number without any units. Keep four decimal places.)

5.5065

n order to determine an interval for the mean of a population with unknown standard deviation a sample of 61 items is selected. The mean of the sample is determined to be 23. The number of degrees of freedom for reading the t value is

60

In order to estimate the average time spent on the computer terminals per student at a local university, data were collected for a sample of 81 business students over a one-week period. Assume the population standard deviation is 1.8 hours. Refer to Exhibit 8-1. If the sample mean is 9 hours, then the 95% confidence interval is

8.61 to 9.39 hours

The fact that the sampling distribution of the sample mean can be approximated by a normal probability distribution whenever the sample size is large is based on the

Central limit theorem

The weight of items produced by a machine is normally distributed with a mean of 8 ounces and a standard deviation of 2 ounces. What is the probability that a randomly selected item weighs exactly 8 ounces?

None of the above

Suppose we try to estimate the average money spend by customers. Two different random samples of 100 data values are taken from the large population. One sample has a larger sample standard deviation than the other. Each of the samples is used to construct a 95% confidence interval. How do you think these two confidence intervals would compare?

With a larger sample standard deviation, the margin of error will be larger, and the confidence interval also will be larger none of the above

A standard normal distribution is a normal distribution with

a mean of 0 and a standard deviation of 1

A continuous random variable may assume

all values in an interval or collection of intervals

A sample of 25 observations is taken from a process (an infinite population). The sampling distribution of p bar is

approximately normal if np ≥ 5 and n(1-p) ≥ 5

A 95% confidence interval for a population mean is determined to be 100 to 120. If the confidence coefficient is reduced to 0.90, the interval for μ

becomes narrower

As the number of degrees of freedom for a t distribution increases, the difference between the t distribution and the standard normal distribution

becomes smaller

Using an α = 0.04 a confidence interval for a population proportion is determined to be 0.65 to 0.75. If the level of significance, α, is decreased, the interval for the population proportion

becomes wider

Excel's NORM.DIST function can be used to compute

cumulative probabilities for a normally distributed x value

A normal probability distribution

is a continuous probability distribution

The sampling distribution of the sample mean

is the probability distribution showing all possible values of the sample mean

The standard deviation of all possible x bar values is called the

standard error of the mean

As the sample size increases, the

standard error of the mean decreases

The standard deviation of p bar is referred to as the

standard error of the proportion

Excel's NORM.INV function can be used to compute

the normally distributed x value given a cumulative probability

In interval estimation, the t distribution is applicable only when

the sample standard deviation is used to estimate the population standard deviation

If we change a 95% confidence interval estimate to a 99% confidence interval estimate, we can expect

the size of the confidence interval to increase

The weight of items produced by a machine is normally distributed with a mean of 8 ounces and a standard deviation of 2 ounces. What is the random variable in this experiment?

the weight of items produced by a machine

__________ is a property of a point estimator that is present when the expected​ value of the point estimator is equal to the population parameter it estimates.

unbiased