Decimals

Decimals are another way to write tenths, hundredths and thousandths. Line up the decimal points to add and subtract. To multiply, ignore the points, multiply, then put back as many decimal places as there were altogether.

Key facts

  • 0.3 is 3 tenths; 0.07 is 7 hundredths.
  • Adding or subtracting: line up the points (fill gaps with zeros).
  • Multiplying: count the decimal places in the question.
  • Dividing by a decimal: multiply both numbers by 10 until it’s a whole number.

Worked examples

Example 1

Work out 4.7 + 12.85.

  1. Write 4.7 as 4.70 so both have two decimal places. 4.70 + 12.85
  2. Add in columns. 17.55

Answer: 17.55

Example 2

Work out 0.6 × 0.4.

  1. Without the points. 6 × 4 = 24
  2. There are 2 decimal places in the question. 0.24

Answer: 0.24

Example 3

Work out 7.2 ÷ 0.3.

  1. Multiply both by 10. 72 ÷ 3
  2. Divide. 72 ÷ 3 = 24

Answer: 24