# Decimal Number System

## Decimal Number System

A positional numeral system that groups objects by ten and uses the digits 0, 1, 2, 3, 4, 5, 6, 7, 8 and 9.

We say that the decimal number system is a base 10 numeral system. Reading numbers in the decimal system uses the written form of digits like onetwothree, etc, but also ten, twenty, thirty, etc., and then one hundredone thousandone million, etc.

### Educational Note

• When they are written, the digits of large numbers are separated into groups of three digits: 380 645 321
However, we make an exception when a number only has 4 digits, like 2014. In this case, the space is optional.
• The digits of decimal numbers are also separated by blocks of three digits: 45.978 097 809 78 …
We add ellipses when the sequence is unlimited: $$\frac{1}{3}$$ = 0.333 333 333 … and $$\frac{1}{8}$$ = 0.125.
• The word form of a number matches the place value of the digits. For compound numbers between twenty-one and ninety-nine we use a hyphen. For example, 3277 is written as three thousand two hundred seventy-seven.