What is a decimal?
A decimal uses a point to show parts smaller than one. The first place after the point is tenths, the second is hundredths. So 0.7 means 7 tenths, and 0.25 means 25 hundredths.
Key idea
When adding or subtracting decimals, line up the decimal points so tenths sit under tenths and hundredths under hundredths.
Adding decimals
Worked example
Add 2.4 + 1.35.
Line up the points and add:
2.40 + 1.35 = 3.75.
Check: 3.75 − 1.35 = 2.40. Correct!
Decimals and fractions
Decimals and fractions are two ways to show the same value: 0.5 = 1/2, 0.25 = 1/4, and 0.75 = 3/4. To compare decimals, first look at the tenths: 0.7 is bigger than 0.65 because 7 tenths is more than 6 tenths. Writing 0.7 as 0.70 makes the comparison clear.
Remember
- First place = tenths, second place = hundredths.
- Line up the decimal points before adding or subtracting.
- 0.5 is the same as one half.