Decimals are another way of writing fractions. Decimals are easier to work with, because we can compare the values of numbers instantly. Doing sums using decimals is also easier than doing them with fractions. When you use a calculator to divide a number into smaller parts, the result will include decimals if that number cannot be divided into whole numbers.

Tenths

We know that when we divide a whole into parts, we get fractions. This shape below, is our whole.

If we divide it into ten equal parts, we get tenths.

Imagine that the whole is the number 1. In decimals, we write a tenth as 0.1.

Adding together two parts or two-tenths, we get 0.2. Adding together three parts or three-tenths, we get 0.3. Three-tenths, ³⁄₁₀ or 0.3 are different ways of writing the same thing.

​​​​​​​Decimal numbers such as 1.7 are made up of a whole number (in this case, 1) and a decimal (in this case, 0.7 or seven-tenths). In fractions, we would write this number as 1 ⁷⁄₁₀ (one and seven-tenths). 

Hundredths

Now let's divide that whole into 100 parts.

Here is a block made up of 100 cubes. The block is the whole and the cubes are each a hundredth of the whole, or 0.01. 30 of the cubes make up thirty-hundredths of the whole, or 0.30.

Adding together two parts or two-hundredths, we get 0.02. Adding together three parts or three-hundredths, we get 0.03. Three-hundredths, ³⁄₁₀₀ or 0.03 are different ways of writing the same thing.

If we added together 25 parts, or twenty-five hundredths, we get 0.25. This is the same as 2 tenths (0.2) plus 5 hundredths (0.05). 

A decimal number may contain whole numbers, tenths and hundreds. The number 6.47, for example, is made up of the whole number 6, 4 tenths and 7 hundredths.

Consultant: Adam Larking