Boba Maths

Year 6 · Arithmetic skills · Skill 4B

Skill 4B: Adding and subtracting decimals with different decimal places

Add and subtract decimals that have different numbers of decimal places.

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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.

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Worked examples

When decimals have different numbers of decimal places, the secret is to line up the decimal points and fill the gaps with zeros. Then it is ordinary column addition or subtraction.

Example 1

Adding

15.3 + 6.482

  1. The numbers have different numbers of decimal places (1 and 3). Add zeros to the shorter one so that both have 3: 15.3 becomes 15.300.
  2. Line up the decimal points and calculate from the right. The added zeros are shown in grey.
    1.
    15.300
    +6.482
    21.782
  3. Column by column:
    • thousandths: 0 + 2 = 2. Write 2.
    • hundredths: 0 + 8 = 8. Write 8.
    • tenths: 3 + 4 = 7. Write 7.
    • ones: 5 + 6 = 11. Write 1 and carry 1 into the tens column.
    • tens: 1 + 0 + 1 = 2. Write 2.
    Put the decimal point directly under the others.
  4. The answer is 21.782.

Answer: 21.782

Example 2

Subtracting

32.4 − 5.867

  1. The numbers have different numbers of decimal places (1 and 3). Add zeros to the shorter one so that both have 3: 32.4 becomes 32.400.
  2. Line up the decimal points and calculate from the right. The added zeros are shown in grey.
    32211.41309010
    −5.867
    26.533
  3. Column by column:
    • thousandths: 10 − 7 = 3. 0 is smaller than 7 and the hundredths column is 0, so exchange across the zero: take 1 from the tenths column, leave 9 in each zero column and make 10 here.
    • hundredths: 9 − 6 = 3.
    • tenths: 13 − 8 = 5. 3 (after lending 1 away) is smaller than 8, so exchange: take 1 from the ones column to make 13.
    • ones: 11 − 5 = 6. 1 (after lending 1 away) is smaller than 5, so exchange: take 1 from the tens column to make 11.
    • tens: 2 − 0 = 2.
    Put the decimal point directly under the others.
  4. The answer is 26.533.

Answer: 26.533

Top tips

  • Line up the decimal points, not the right-hand digits.
  • Fill empty places with zeros so every row has the same length.
  • Estimate by rounding to whole numbers first.

Watch out for

  • Lining up the last digits, so tenths are added to hundredths.
  • Dropping the decimal point from the answer.

Try some questions

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

  1. 8.4 + 3.7 =
    Show the answer

    12.1

  2. 43.6 + 7.56 =
    Show the answer

    51.16

  3. 84.2 + 7.943 =
    Show the answer

    92.143

  4. 94.381 + 7.683 =
    Show the answer

    102.064

All arithmetic skills

Skill 1ASkill 1BSkill 2ASkill 2BSkill 3ASkill 4ASkill 5ASkill 5BSkill 6ASkill 6BSkill 6CSkill 6DSkill 7ASkill 8ASkill 9ASkill 10ASkill 10BSkill 10CSkill 11ASkill 11BSkill 11CSkill 12ASkill 13ASkill 14A

Arithmetic skills overview · Year 6 overview