Decimal place value
A decimal point separates whole numbers from parts smaller than one. The first place after the point is tenths, the second is hundredths. In 5.34 the 3 means 3 tenths (0.3) and the 4 means 4 hundredths.
Key idea
To add or subtract decimals, line up the decimal points so tenths sit under tenths and hundredths under hundredths.
Worked example
Worked example
Work out 2.6 − 1.4.
Line up the points and subtract: 2.6 − 1.4 = 1.2.
Check: 1.2 + 1.4 = 2.6. ✓
Multiplying and dividing by 10
To multiply by 10, move the digits one place left: 0.7 × 10 = 7. To divide by 10, move them one place right: 4.5 ÷ 10 = 0.45. Decimals and fractions are linked: ½ is the same as 0.5 because ½ = 5/10. When you round a decimal to one decimal place, look at the hundredths digit; if it is 5 or more, round the tenths digit up, so 6.48 rounds to 6.5.
Remember
- Line up decimal points when adding or subtracting.
- × 10 moves digits left; ÷ 10 moves digits right.
- To round to 1 decimal place, look at the hundredths digit.