AP CSP Assessment 1

Which of the following best describes how computing devices represent information?

• A. A computer will either represent information as bits or bytes but not both

• B. A computer represents data as a byte which is either a 0 or a 1

• C. A computer represents data as bits which is either a 0 or a 1

• D. A computer represents information as bits which contain 8 bytes.

Answer explanation

Explanation: The definition of a bit: a contraction of "Binary Digit"; the single unit of information in a computer, typically represented as a 0 or 1.

This came up in Lesson 4 - Binary Numbers

When visiting a museum Lian takes a photo of a painting with a smartphone which stores the photo as an image file. Which of the following best describes the differences between the painting itself and the photo of the painting stored on the smartphone?

• A. Both the painting and the photo are analog

• B. The photo is a digital representation of the analog painting

• C. Sampling can be used to determine whether the analog image is an accurate representation of the painting

• D. The phone can represent the photo in either digital or analog formats depending on the sampling technique that is used

Answer explanation

Explanation: A painting is an analog because it's something with continuous representation. A digital photo changes discreetly at every pixel using a finite set of colors.

The came up in Lesson 7 - Black and White Images

Your computer uses 4 bits to represent decimal numbers (0, 1, 2, 3 and so on) in binary. What is the SMALLEST number for which an overflow error occur?

• 14

• 15

• 16

• 17

Answer explanation

Explanation: The 4-bit binary number 1111 represents the decimal number 15. Counting up to the next number, 16, will cause the 4-bit binary number to overflow

Overflow was covered in Lesson 5 - Overflow and Rounding

Which of the following is true of how computers represent numbers?

• Using a fixed but large number of bits can eliminate the possibility of round off error when representing numbers in binary

• With a fixed number of bits some numbers are too large to represent in a computer which will lead to overflow errors.

• Using a fixed but large number of bits, for example 128, eliminates the possibility of overflow errors.

• With a large but fixed number of bits it is possible to eliminate either round-off errors or overflow errors, but not both.

Answer explanation

Explanation: With a fixed amount of bits, no matter how many, at some point the largest possible value will be reached, with 1s for all the bits. Representing the next largest number will lead to an overflow error and will start back at all 0s.

Lesson 5 - Overflow and Rounding

Convert the binary (base-2) number 1001 to decimal (base-10).

• 9

• 10

• 16

• 17

Convert the decimal (base-10) number 20 to binary (base-2).

• 10010

• 00101

• 11000

• 10100

Which of the following binary (base-2) numbers is LARGEST?

• 11000000

• 01111111

• 00000001

• 10111111

How many total numbers can be represented with an 8-bit binary (base-2) system?

• 127

• 128

• 255

• 256

Answer explanation

Binary is a base 2 number system. With each new bit, we double the amount of unique numbers we can make. With 7 bits, we can make the decimal numbers 0 to 127 (0000000 to 1111111), for a total of 128 unique numbers. When we go up to 8 bits, we can make the decimal numbers 0 to 255 (00000000 to 11111111) for a total of 256 unique numbers.

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

• Lossy compression algorithms are used when perfect reconstruction of the original data is important.

• Lossy compression algorithms are typically better than lossless compression algorithms at reducing the number of bits needed to represent a piece of data.

• Lossless compression algorithms are only used to compress text data.

• Lossless compression algorithms only allow for an approximate reconstruction of the original data.

Jorge is sending a large image file to a friend as part of a shared classroom project. Which of the following is most likely true if Jorge opts to compress the image before sending it?

• The image can no longer be represented using bits.

• The image will have been converted into an analog form.

• The image will require more pixels to display it on the screen.

• The image will require fewer bits in order to be represented.