Reading, writing and breaking down a decimal number

How to read a decimal number correctly

To read 15.6 aloud, you say “fifteen point six”, not “fifteen six”. For a number such as 8.05, you say “eight point zero five”: the zero after the decimal point counts; it indicates that there are no tenths.

Breaking down a decimal number

Breaking down a number means separating it according to the value of each digit. Example using 42.309:

• 4 tens -> 40
• 2 ones -> 2
• 3 tenths -> 0.3
• 0 hundredths -> 0.00
• 9 thousandths -> 0.009

We write: 42.309 = 40 + 2 + 0.3 + 0.009

It can also be written as a fraction: 42.309 = 42,309/1,000.

Zeros that don’t change anything… or almost nothing

• Adding a zero at the end of the decimal part does not change the value of the number: 5.4 = 5.40 = 5.400.
• Adding a zero at the start of the whole number part doesn’t change anything either: 05.4 = 5.4.
• However, a zero between the decimal point and another digit makes a huge difference: 5.04 is very different from 5.4!

Summary table

Written form	Pronunciation	Value as a fraction
0.5	zero point five	5/10
0.05	zero point zero five	5/100
3.20	three point twenty (= three point two)	320/100 = 32/10

A common pitfall to avoid

Many pupils think that 3.20 is greater than 3.2 because it has ‘more digits’. This is incorrect: 3.20 and 3.2 represent exactly the same value, as 20 hundredths = 2 tenths.