Decimal number system

Decimal (also called Base-10, denary, and decenary) is a positional numeral system which can represent every number using 10 digits [0,1,2,3,4,5,6,7,8,9] each of which represent a number from zero through nine. Higher numbers are represented using number places whose values are 10 times bigger than the previous place which can be added with smaller number places to create a large number. If a digit is inserted in to a number place, then the value of the number place gets multiplied by the digit. For instance the decimal number 432 is comprised of 4 times one hundred (ten squared), 3 tens, and 2 ones (ten to the 0th).

A decimal radix point, typically a period, is used to represent number places smaller than one, with "0.1" representing a tenth, "0.01" representing a hundredth and so on.

Usage
Decimal has become the most popular base for numbers in languages, and is almost always used to represent numbers, with the zero-included version being first adopted by the Indians in AD 224 or earlier. This may be for a variety of different reasons, although the most commonly accepted theory is that people 10 fingers on both hands which makes finger-counting in decimal fairly easy.

Base Theory
As for fractions and arithmetic, 10 is a semiprime (the product of 2 primes), which makes it have just 2 non-trivial divisors [2,5].

These numbers are the only numbers with pattern in their times table, and the only fractions that terminate in decimal have the product of a power of 2 and a power of 5 in their denominator, which makes it difficult to convert between fractions and decimals in decimal. This somewhat can be avoided by using rounding, long division, and repeating notation. The decimal omega 9 is divisible by 3, which makes thirds have only one repeating digit 3.

Unit fractions 1/2-16 in decimal