What is a decimal?
Year 4 introduces tenths and hundredths, Year 5 thousandths, and Year 6 works with numbers to three decimal places. Below: what it means, a worked example, the mistake to watch for and an 11+ question.
The answer
A decimal is a number with a decimal point, where the digits after the point show parts of a whole.
What it means
The first digit after the point is tenths, the next is hundredths and the next is thousandths. 3.47 is 3 ones, 4 tenths and 7 hundredths.
Some decimals are worth learning by heart: 0.5 = ½, 0.25 = ¼, 0.75 = ¾ and 0.1 = 1/10.
A worked example
Order 0.7, 0.65 and 0.072, smallest first
- Compare the tenths digit first: 0, 6 and 7 tenths.
- 0.072 has 0 tenths, 0.65 has 6 tenths and 0.7 has 7 tenths.
- In order: 0.072, 0.65, 0.7.
The common mistake
Thinking a longer decimal is bigger. 0.65 looks bigger than 0.7, but 0.7 = 0.70, and 70 hundredths is more than 65 hundredths.
How it comes up in the 11+
Which is larger, 0.3 or 0.29? By how much?
Answer: 0.3, by 0.01
- Write both with two decimal places: 0.30 and 0.29.
- 30 hundredths is more than 29 hundredths, so 0.3 is larger.
- 0.30 − 0.29 = 0.01.
Try it yourself
The chart opens on 3.47 from the explanation. Multiply by 10 or 100 and watch the tenths and hundredths move up into whole-number columns. It stops at hundredths, as Year 4 does, so it cannot show thousandths like the 2 in 0.072.
Multiplying by 10 moves every digit one column to the left: 3.47 × 10 = 34.7.
Related words and practice
More maths words
Questions parents ask
Is 0.5 the same as ½?
Yes. 0.5 is 5 tenths, and 5/10 simplifies to ½.
How do you say 3.25 out loud?
"Three point two five". Saying "three point twenty-five" is a common slip that hides the place value of each digit.
Knowing the words is half of an 11+ maths question
11+ papers use maths vocabulary without explaining it. The free diagnostic checks maths, English and both kinds of reasoning, and shows what to practise next. No card is required.