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Mathematics · Grades 3–5

Complete one whole

Keep the common denominator while finding the missing numerator.

Make a worksheet

The key idea

Keep the common denominator while finding the missing numerator.

a/b + (b − a)/b = 1

Worked examples

17/20 + □ = 1

17/20 + 3/20 = 20/20 = 1

3/20

4/5 + □ = 1

4/5 + 1/5 = 5/5 = 1

1/5

Try it yourself

  1. 1/5 + □ = 1

  2. 1/10 + □ = 1

Check your understanding

Answers and marking notes
  1. 4/5

    1/5 + 4/5 = 5/5 = 1

  2. 9/10

    1/10 + 9/10 = 10/10 = 1

Further reading and review references

These are reference links, not copied exercises, institutional endorsement or proof of independent review.

Learning preview · teacher review required. Grade bands are approximate, not official curriculum alignment.