1
a The binary system of numbers is used to store values in a computer.
b We normally count using the decimal number system.
c One digit in a binary number is called a bit.
d Because binary numbers are difficult to work with, a system called octal, which contains the digits 0 to 7, is used.
e The hexadecimal number system uses the letters A to F to represent some of the digits.

2 Digital computers store data as zeros and ones. Since there are only two digits in this system, it is known as the binary number system. The binary number system is inconvenient to use, so the octal system based on 8 and the hexadecimal number system based on 16 are also used by programmers.
3
a 10012
b 1 00012
c 1 11102
d 101 10012
e 1111 10002
4
a 118
b 218
c 368
d 1318
e 3708
5
a 916
b 1116
c 1E16
d 5916
e F816
6
a 510
b 1310
c 20310
7
a 1310
b 3110
c 13410
d 51110
8
a 2110
b 7510
c 19210
d 27010
9
a 11012 , D16
b 1 11112 , 1F16
c 1000 01102 , 8616
d 1 1111 11112 , 1FF16
10 Binary numbers were chosen because it is relatively easy to construct devices that can distinguish between on (1) and off (0) and also process strings of pulses.
11 Long binary strings are unwieldy. It is much easier for humans to work with the shorter strings that hexadecimal notation produces.