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 / 要点
When adding or subtracting decimals, line up the decimal points so tenths sit under tenths and hundredths under hundredths.
Adding decimals
Worked example / 例题
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 / 记住
- First place = tenths, second place = hundredths.
- Line up the decimal points before adding or subtracting.
- 0.5 is the same as one half.