Decimal

Decimal is the predominant numeral system used by humans, though some cultures do or did use other number systems. This is almost certainly because humans have ten fingers; digit is also the anatomical term referring to fingers and toes.

Computers use other number systems and so, sometimes, do people using computers. Binary, octal and hexadecimal are common, because they are easy to implement on a computer. Humans' use of decimal gave rise to binary-coded decimal in the context of computers.

Fractions

Ten is the product of the first and third prime number and is one greater than the square of the second prime number. This leads to plenty of simple decimal fractions:

1/2 = 0.5

1/3 = 0.3333 recurring

1/4 = 0.25

1/5 = 0.2

1/6 = 0.16666 recurring

1/8 = 0.125

1/9 = 0.1111 recurring

Prime factors other than 3 may give longer repeating sequences, see for instance 7, 11, 13.

See also decimal point, Dewey Decimal System.