AP Computer Science Principles Units 1, 2 & 3

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

• The binary number system is the only system flexible enough to allow for representing data other than numbers.

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

• It typically takes fewer digits to represent a number in binary when compared to other number systems (for example, the decimal number system)

• It's impossible to build a computing machine that uses anything but binary to represent numbers

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

• 0010

• 1010

• 0110

• 0101

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?

• 2 Bits

• 3 Bits

• 5 Bits

• 6 Bits

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?

• At one of the lowest levels of abstraction, all digital data can be represented in binary using only combinations of the digits zero and one.

• The same value (number) can have a different representation depending on the number system used to represent it.

• Groups of bits can be used to represent abstractions, including but not limited to numbers and characters.

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

Consider the following three binary numbers:

01010 010000 1110

Which of the following lists the numbers in order from least to greatest?

• 010000, 1110, 01010

• 01010, 1110, 010000

• 01010, 010000, 1110

• 1110, 01010, 010000

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.

• Double the number of bits in studentID to double the number of IDs that the database can represent

• Keep using an 8-bit number for studentID but reserve the first bit to indicate middle school or high school.

• Remove a bit from studentID to make room for incoming students

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

• Bit-rate (bandwidth) is the time elapsed between the transmission and receipt of a piece of digital data.

• Latency is the amount of data (measured in bits) that can be sent in a fixed amount of time.

• Digital data can only be transmitted between two devices when they are physically connected to one another (for example by a copper wire)

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

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

• 10 Bits

• 16 Bits

• 17 Bits

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: A

• ASCII Character: B

• ASCII Character: D

• The table does not contain the value represented by the binary number 0100 0010

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?

• 2¹ = 2 times as many values

• 2²= 4 times as many values

• 2³ = 8 times as many values

• 2⁴ = 16 times as many values