Boba Maths

Year 6 · Arithmetic skills · Skill 7A

Skill 7A: Multiplying decimals by whole numbers

Multiply decimals with up to 2 decimal places by 1-digit and 2-digit whole numbers.

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Each file is an editable Word document (.docx) with 25 questions in five columns. It opens in Word, Google Docs, Pages and LibreOffice, so you can change questions or add working space before printing.

Download the worksheet Download the answers Generate a new sheet for this skill

Worked examples

To multiply a decimal by a whole number, remove the decimal point, multiply as whole numbers, then put the decimal point back by dividing by the same power of 10.

Example 1

One decimal place

4.6 × 13

  1. Estimate first: 4.6 is close to 5. 5 × 13 = 65, so the answer should be near 65.
  2. Ignore the decimal point for now. 4.6 has 1 decimal place, so it is 46 ÷ 10. Multiply the whole numbers: 46 × 13.
       46
 × 13
-----
  138   ← 46 × 3
  460   ← 46 × 10
-----
  598
  3. Now put the decimal point back. We multiplied by 10 to remove it, so divide the answer by 10: 598 ÷ 10 = 59.8.
  4. So 4.6 × 13 = 59.8. This is close to the estimate of 65, so it is sensible.

Answer: 59.8

Example 2

Two decimal places

3.45 × 18

  1. Estimate first: 3.45 is close to 3.5. 3.5 × 18 = 63, so the answer should be near 63.
  2. Ignore the decimal point for now. 3.45 has 2 decimal places, so it is 345 ÷ 100. Multiply the whole numbers: 345 × 18.
       345
  × 18
------
  2760   ← 345 × 8
  3450   ← 345 × 10
------
  6210
  3. Now put the decimal point back. We multiplied by 100 to remove it, so divide the answer by 100: 6,210 ÷ 100 = 62.1.
  4. So 3.45 × 18 = 62.1. This is close to the estimate of 63, so it is sensible.

Answer: 62.1

Top tips

  • Count the decimal places in the question; the answer has the same number (before removing any trailing zeros).
  • An estimate tells you whether the decimal point is in the right place.
  • Use a formal method for the whole-number multiplication.

Watch out for

  • Putting the decimal point in the wrong place.
  • Forgetting to divide by 10 or 100 at the end.

Try some questions

These are from the worksheet. Work each one out, then open it to check.

  1. 3.7 × 8 =
    Show the answer

    29.6

  2. 15 × 4.2 =
    Show the answer

    63

  3. 3.75 × 32 =
    Show the answer

    120

  4. 64 × 1.75 =
    Show the answer

    112

All arithmetic skills

Skill 1ASkill 1BSkill 2ASkill 2BSkill 3ASkill 4ASkill 4BSkill 5ASkill 5BSkill 6ASkill 6BSkill 6CSkill 6DSkill 8ASkill 9ASkill 10ASkill 10BSkill 10CSkill 11ASkill 11BSkill 11CSkill 12ASkill 13ASkill 14A

Arithmetic skills overview · Year 6 overview