When doing calculations, decimals are easier to work with than fractions because we can compare the values of numbers instantly. We can add, subtract, divide and multiply decimals and decimal numbers just like whole numbers. It is useful to understand place value when doing sums with decimals.

To find out the decimal equivalent of a half (½), take a shape made up of 100 blocks. Divide the shape in two (halve it) and count the blocks. There are 50. So a half is the same as 50 hundredths. Use place value to write this as a decimal: 0.50. This is the decimal equivalent of a half. We often leave off the last 0, so it is written 0.5.
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Now follow the same steps to work out the decimal equivalent of a quarter (¼). This time the shape is divided into four equal parts. There are 25 blocks in each, so this means a quarter is the same as 25 hundredths. Written as a decimal this is 0.25.
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To work out the decimal equivalent of three-quarters (¾), take three of those four equal parts, each made up of 25 blocks. You can either add them up or multiply 25 by 3 to get the same total, 75. This means three-quarters is the same as 75 hundredths. Its decimal equivalent is 0.75.
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Sums with decimals

You can add or subtract decimal numbers in the same way as you would add or subtract whole numbers. An example of an addition sum is this: 2.1 + 3.4 = 5.5. An example of a subtraction sum is this: 6.7 - 3.4 = 3.3.

This is an example of an addition sum using numbers with two decimal places: 4.56 + 5.32 = 9.88.

Dividing and multiplying by 10 or 100

When you divide a number by 10, you slide that number one place to the right. So, using whole numbers, 50 ÷ 10 = 5. You do the same for decimals: 5 ÷ 10 = 0.5 (slide the 5 one place to the right, this time to the right of the decimal point).

When you divide a number by 100, you slide that number two places to the right: 5 ÷ 100 = 0.05.

To multiply numbers by 10, slide the number one place to the left. 2.3 x 10 = 23.0 (or just 23).

When multiplying a number by 100, slide the number two places to the left. 0.47 x 100 = 47.00 (or just 47).