Computer Science Principles Unit 1,2,4 Code.org

What is the digital divide? Which of the following is the most accurate description of what is known as the "digital divide". The digital divide is about how...

...people's access to computing and the Internet differs based on socioeconomic or geographic characteristics.

Consider the following three binary numbers: 01010 010000 1110 Which of the following lists the numbers in order from least to greatest?

01010 1110 010000

A binary message consisting of four bits was sent to you by a friend. The message was supposed to be ABAB. Unfortunately, your friend set the bit on the wire once every 2 seconds, but you read the wire once every second. Assuming that the first bit was sent and read at the same time, what message did you receive instead?

AABB

ASCII is a character-encoding scheme that uses a numeric value to represent each character. For example, the uppercase letter "G" is represented by the decimal (base 10) value 71. A partial list of characters and their corresponding ASCII values are shown in the table below. ASCII characters can also be represented by binary numbers. According to ASCII character encoding, which of the following letters is represented by the 8-bit binary value: 0100 0010

ASCII Character: B

The Chart below from Google Trends shows the prevelance of some search terms in the United States between 2004 and the present. Which of the following is the most accurate statement of what this chart is showing

Generally speaking, since 2009 more people use "red" in their search terms more than they use "blue", "yellow", "green", or "purple"

Below is an image from Google Trends that plots Cats and Dogs. Choose the most accurate description of what this data is actually showing based on what you know about how Google Trends works

People search for "dogs" more frequently than "cats"

Which of the following is true about the way digital data is transmitted on the Internet?

Two devices must communicate using the same bit-rate to successfully send and receive digital data

According to the domain name system (DNS), which of the following is a subdomain of the domain example.com?

about.example.com

To improve communication in playing battleship on the Internet Simulator your group invented a(n):

protocol

Choose Two: Identify the two true statements about HTTP.

1 An HTTP request is sent from a client to request access to data stored on a server. 2 Displaying a web page will often require multiple HTTP requests in order to acquire all the necessary data.

Approximately how much bigger (how many more bytes) is a megabyte than a kilobyte?

1,000 times bigger

Which two of the following statements are true about routing on the Internet.

1. A packet travelling between two computers on the Internet may be rerouted many times along the way. 2.A packet contains addressing information to allow routers to decide how best to forward along that packet towards its destination.

Choose the two best answers to complete the sentence: If I understand how the internet works then I will be able to:

1.Make informed choices to support or oppose decisions my government makes about access to the internet. 2.Make informed choices about my privacy on the internet.

Why is the Vigenere cipher hard to crack? (select 2

1.One cannot solve using frequency analysis directly. 2. The key length is variable and potentially very long

On a survey of high school seniors they are asked: What state do you live in? How likely are you to attend college in your home state? (on a scale of 1-5, 5 meaning "very likely") What do you plan to study? A student, Amara, plans to use the survey data to create a visualization and short summary of students' plans for college. First she wants to learn more about how the data was collected. Of the following things she might learn about the survey, which are the most likely sources of bias in the results based how it was collected? Choose two answers.

1.She learns that responses were collected only by mobile app. 2.She learns that the survey was only available to students who scored at the top 10% on the PSAT.

Pick Two: Pick the two statements about packets and routing on the Internet which are true.

1.TCP ensures messages can be reliably transmitted across the Internet 2.TCP must account for the fact that packets may not arrive at a destination computer in the intended order

If the post office delivered mail exactly like routers deliver messages on the internet, which 2 of the following statements would be true?

1.The mailman would sometimes take a different path to deliver each letter to your home. 2. Letters would be written on the outside of envelopes for all to read instead of letters put inside envelopes.

What is the 4-bit binary number for the decimal number Ten (10)?

1010

What is 13 MOD 17?

13

You have a coordinate grid that is 96 x 96. Assuming that you encode the x and y coordinate as separate numbers, what is the minimum number of bits that you will need to encode a coordinate in that space?

14

When responding to a question with 4 choices, the most efficient method will require _____ number of bits.

2 bits

Two students have developed a protocol in which they send 4-bit messages to each other. They decide to modify their protocol to start sending 8-bit messages instead. How many more values can be represented in an 8-bit message than a 4-bit message?

24 = 16 times as many values

How many bits? ASCII has an encoding for every character of the alphabet as well as encodings for numbers -- that is, encodings for the symbols of the digits 0-9. So here is a trick question: How many bits are required to store the text of the number "150" in ASCII?'

24 bits

The Caesar Cipher has 25 different shifts to try. How many possibilities are there to try in a random substitution cipher?

26 x 25 x 24 x***x 3 x 2 x 1

A video-streaming Web site uses 32-bit integers to count the number of times each video has been played. In anticipation of some videos being played more times than can be represented with 32 bits, the Web site is planning to change to 64-bit integers for the counter. Which of the following best describes the result of using 64-bit integers instead of 32-bit integers?

2^32 times as many values can be represented.

How many bytes does it take...? How many bytes (or bits) are required to encode an image that is 25 pixels wide and 50 pixels tall, if you encode each pixel with 3 bytes (24 bits) of RGB data. (Don't forget to add in the metadata! -- you should assume that we are using the file format used in this lesson with metadata that had 1 byte each for width, height and bits-per-pixel.)

3,753 bytes (30,024 bits)

The world is currently in a transition to using IPv6, a newer version of the IP protocol that uses 128-bit addresses instead of 32-bit addresses used by IPv4. What is the main problem that IPv6 was created to solve?

32-bit addresses could not ensure that every internet-connected device can receive a unique IP address

What is 20 MOD 15?

5

What is the minimum number of bits you need to encode the 26 letters of the alphabet plus a space?

5 bits

What is the minimum number of bits you would need to encode the 26 letters of the alphabet plus a space - a total of 27 characters?

5 bits

How many unique IP addresses could be made in a fixed-length IP address system using 6 bits?

64 Users

The standard QWERTY keyboard has 47 keys that can place characters on the screen. Each of these keys can also display a second character by holding the "Shift" key at the same time. How many bits would you need to encode everything that could be typed on this keyboard?

7 bits

If you just had two shapes (say, a circle and a square), how many 3-place patterns could you make?

8

Pick the two expressions involving the Modulo operation that compute to the exact same value (choose 2)

9 MOD 8 1 MOD 16

8 bits is enough to represent 256 different numbers. How many total bits do you need to represent 512 (twice as many) numbers?

9 bits

Choose the answer that is NOT a feature of Public Key Cryptography:

A Public Key database ensures 3rd party accountability of security

The Internet Engineering Task Force (IETF) defines the protocols and standards for how the Internet works. The members of the IETF are:

A loosely organized collection of citizens and engineers

The Internet Engineering Task Force (IETF) defines the protocols and standards for how the Internet works. The members of the IETF are:

A loosely organized collection of citizens and engineers who communicate mostly by email.

Which of the following is NOT true about packets?

A message sent across the Internet can always be contained in a single packet

A binary question is defined as:

A question which can be answered in only one of two possible ways

A middle school is expanding to open a high school next year, doubling the total number of students. The school keeps a database in which each student's unique ID number is stored as an 8 bit number called studentID. Before the arrival of the new students almost every 8 bit number has already been assigned to a student. Of the options provided below, which is the smallest change to the way studentID is represented necessary to ensure each incoming student receives a unique ID?

Add a bit to studentID to double the number of IDs that the database can represent.

What is a Distributed Denial of Service (DDoS) attack?

An attempt to compromise a single target by flooding it with requests from multiple systems.

Which of the following statements are true about routers and routing on the Internet. Choose two answers.

C. A packet traveling between two computers on the Internet may be rerouted many times along the way or even lost or "dropped". D. Routers act independently and route packets as they see fit.

Which of the following statements is the LEAST TRUE about personal data that technology companies potentially collect about their users?

Companies are required by law to give users options to personalize what data they collect about them

The figure represents a network of physically linked computers labeled A through F. A line between two computers indicates that the computers can communicate directly with each other. Any information sent between two computers that are not directly connected must go through at least one other computer. The weight or cost of sending information from one computer to another is indicated by the number above the line. For example, information can be sent directly between computers A, and B and will cost 5. Information sent between computers A and D must go through either computer C (with total cost 5), or through computer B (with total cost 8) Question: Computer A sends a packet intended to reach computer F. Along its path it arrives at Computer C. Which computer should Computer C forward the packet to in order to use the most cost effective path?

Computer D

An artist makes an RGB raster image in which each pixel color is encoded with 12-bits --- 4 bits each for red, green and blue. Which of the following correctly shows the hexadecimal value for Red as a 12-bit representation.

F00

The various protocols in use on the internet are said to operate in layers in which the protocol(s) at each layer solve one problem related to networked communication, and higher layers are built on top of, and rely on, the lower layers to do their jobs. From the list provided choose the two (2) answers that correctly describe which internet protocol relies on the other. For example: if protocol A relies on protocol B, it means that A is a higher level protocol than B, and thus protocol B must exist and work properly in order for protocol A to do its job. Select two answers.

HTTP relies on TCP/IP DNS relies on TCP/IP

HTTP is considered to be a high level protocol because:

HTTP requests make use of abstractions provided by lower level protocols.

What feature of DNS and IP allow the internet to scale?

Hierarchy

Which of the following are true statements about digital certificates in Web browsers? I. Digital certificates are used to verify the ownership of encrypted keys used in secured communication II. Digital certificates are used to verify that the connection to a Web site is fault tolerant.

I only

How does a computer resolve a domain name into an IP address?

It asks a DNS server for the corresponding IP address

What is the best explanation for why digital data is represented in computers in binary?

It's easier, cheaper, and more reliable to build machines and devices that only have to distinguish between binary states.

A compression scheme for long strings of bits called run-length encoding is described as follows: Rather than record each 0 and 1 individually, instead record "runs" of bits by storing the number of consecutive 1s and 0s that appear. Since it's binary, any run of 0s must be followed by a run of 1s (even if the run is only 1-bit long) and vice versa. Thus, you can store a list of small numbers that represents the alternating runs of 0s and 1s. Here is an example: To uncompress the data back into its original binary state, you simply reverse the process. This technique is an example of what type of compression?

Lossless compression

Which of the following is true of lossy and lossless compression techniques?

Lossless compression is fully reversible, meaning the original file can be recreated bit for bit.

The colors of the pixels in a digital image are often represented by red, green, and blue values between 0 and 255 (an RGB triplet). A photographer is manipulating a digital image to lighten it because all of the RGB values in the image are less than 100, making it very dark. He does this by adding 20 to the R, G, and B values of each pixel, then overwriting the original image. What type of transformation is the photographer using on the digital image?

Lossless transformation

A raw digital sound file samples a sound wave at some interval and measures the height of the wave at each point. Thus, raw sound is recorded as a list of numbers. In very broad terms the MP3 audio compression algorithm identifies frequencies and volume levels - low and high - that are outside the range of human hearing and removes the data representing these frequencies from the original. This technique results in a smaller audio file that sounds exactly the same to the human ear. This technique is an example of what type of compression?

Lossy compression

Which of the following is true of lossy and lossless compression techniques?

Lossy compression is best suited for situations where some loss of detail is tolerable, especially if it will not be detectable by a human.

Which of the following BEST describes how protocols on the Internet (e.g. IP, TCP, HTTP) make use of abstraction to accomplish their respective purposes?

Low level protocols can provide functionality to high level protocols without revealing the details of how this is accomplished.

Historically it has been observed that computer processing speeds tend to double every two years. This is known as:

Moore's Law

Which of the following most accurately describes Moore's Law:

Moore's Law is the observation that computing power tends to double every two years

Which of the following statements best describes the properties of public key encryption?

Public key encryption is an encryption method which relies on separate keys for encrypting and decrypting information.

What is an RFC?

Request For Comments

The AP CS Principles framework contains the following statement: 7.1.1G Search trends are predictors. Which of the following is the most accurate statement about using search trends as predictors of future events?

Search trends are imperfect predictors of future events that may not fully represent society at large.

Number systems with different bases such as binary (base-2) and decimal (base-10) are all used to view and represent digital data. Which of the following is NOT true about representing digital data?

Some large numbers cannot be represented in binary and can only be represented in decimal.

Fill in the blank of the following statement: "______ encryption is a method of encryption involving one key for both encryption and decryption."

Symmetric

Which of the following is NOT true about TCP/IP packets?

TCP guarantees that no packets are ever dropped

In the Internet Simulator, your router knows to send your message to a different router because:

The first 4 bits of the address specify the router number that your friend is on.

A programmer is writing a system that is intended to be able to store large amounts of personal data. As the programmer develops the data system, which of the following is LEAST likely to impact the programmer's choices in designing the structure of the system?

The frequency of a particular item occurring in a data set.

What is the "key" to a Caesar Cipher that someone needs to know (or discover) to decrypt the message?

The number of characters to shift each letter in the alphabet.

A single central register of IP addresses and names (a DNS style system) is an efficient means of translating human readable names to IP addresses. Which of the following is NOT solved by DNS?

There are too few IP addresses to meet the current demand.

Which of the following is a true statement about data compression?

There are trade-offs involved in choosing a compression technique for storing and transmitting data.

When a computer scientist uses the term "Big Data" what do they typically mean?

There is enough data that traditional data processing applications are inadequate.

Which of the following information is not necessary in your protocol to play battleship?

Time of Day

Under which of the following conditions is it most beneficial to use a heuristic approach to solve a problem?

When the problem cannot be solved in a reasonable time and an approximate solution is acceptable

A school starts tracking which websites each computer in the school is visiting by monitoring the packets leaving the school. A sample of the information they have collected appears below: IP Address Time URL ... ... ... 1.1.1.1 11:05:23.22 example.com 1.5.1.8 11:05:29.71 news.com 1.1.5.1 11:06:13.48 sports.com 1.5.1.8 11:08:09.95 example.com ... ... ... 1.1.5.1 17:04:29.20 news.com Which of the following is MOST likely to be answerable using all the data collected by this monitoring?

Which websites are most frequently visited before and after school hours from a school computer

A coffee shop is considering accepting orders and payments through their phone app and have decided to use public key encryption to encrypt their customers' credit card information. Is this a secure form of payment?

Yes, public key encryption is built upon computationally hard problems that even powerful computers cannot easily solve.

Which of the following scenarios is most characteristic of a phishing attack.

You get an email from the IT support desk that asks you to send a reply email with your username and password to verify your account

Select the answer that lists the units of bytes in ascending order (from smallest to largest)

kilobyte, gigabyte, terabyte

The image below shows an encoding for a black and white pixel image. The first two bytes of the data (circled in red) are used to encode the width and height of the image. What is the best term for this type of "data about the data"?

metadata