Decimals as parts of one — Mathematics, 7–10 years
A decimal records tenths and hundredths, placing parts smaller than one on the same number line as whole numbers.
Parts after the point
The digits after the decimal point show parts of one: the first place is tenths and the second is hundredths. So 0.4 means four tenths, while 0.04 means four hundredths, a much smaller amount.
Why decimals?
Whole numbers cannot name every measurement, price, or amount between two marks. Decimals let us describe those gaps clearly, using place value: each step to the right divides the unit into ten times smaller parts.
Compare 0.7 and 0.65
Write 0.7 as 0.70 by adding a zero at the end; its value does not change. Now compare hundredths: 70 hundredths is greater than 65 hundredths. Therefore 0.7 is greater than 0.65.
More digits does not mean more
It feels natural to think 0.65 is larger than 0.7 because 65 is larger than 7. But the digits are in different place values. Compare 65 hundredths with 70 hundredths, or line them up as 0.65 and 0.70.
Money and measuring
Prices such as 2.50 euros and measurements such as 1.25 metres use decimals every day. The same place-value idea lets you read a ruler, compare prices, and work out how much remains after using part of a litre.
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