What is a decimal?
A decimal uses a dot to show parts smaller than 1. The first place after the dot is tenths, the next is hundredths.
Key idea
A tenth is the same as one part out of ten. So 3/10 = 0.3 and 25/100 = 0.25.
Adding and subtracting
Line up the dots, then add or subtract as usual. Keep the dot straight underneath.
Worked example
2.4 + 1.3
Line up the dots: 2.4 and 1.3.
Add: 2.4 + 1.3 = 3.7.
Check: 3.7 − 1.3 = 2.4. Correct!
Comparing decimals
Compare the tenths first. 0.9 has 9 tenths and 0.6 has 6 tenths, so 0.9 > 0.6.
We read 3.7 as "three point seven". The whole-number part is 3 and the tenths part is 7. Money uses two decimal places, like RM2.50, because 1 sen is one hundredth of a ringgit.
When a decimal has no digit in a place, we can write a zero to help. So 0.5 is the same as 0.50, which makes adding 0.25 + 0.5 easier.
Remember
- First place after the dot = tenths.
- Second place = hundredths.
- Line up the dots before adding.