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Missing Number Problems

Maths: Year 3 & 4 National Curriculum, topic 1.2.5

Missing Number Problems

We can use our knowledge of number relationships, number facts and inverse operations to find the missing number in a calculation.

Equations

Equations

  • An equation is a number sentence with an = sign.
  • The = sign just means one side is equal to the other.
  • 3 + 6 = 10 - 1
  • 3 + 6 = 9 and 10 - 1 = 9, so both sides are equal.
Missing number

Missing number

  • Sometimes we have to work out the missing number in an equation.
  • This is not always the number after the = sign.
  • For example:
  • 20 + ? = 50
  • 3 + ? = 10 - 1
Number facts

Number facts

  • We can use our knowledge to help find the missing number.
  • 200 + 400 = ?
  • We know the number fact:
  • 2 + 4 = 6
  • The missing number is 600.
Bar models

Bar models

  • We can use bar models to find the missing number.
  • 20 + ? = 50
  • We can see a relationship between 50, 20 and 30.
  • The missing number is 30.
Inverse operations

Inverse operations

  • We can use inverse operations to find the missing number.
  • 27 + ? = 38
  • The inverse is 38 - 27 = 11.
  • The missing number is 11.

Test yourself on Missing Number Problems

  • Using the bar model, what is the missing number?
    35 + ? = 60

  • Using the bar model, what is the missing number?
    50 − ? = 40

  • Using the bar model, what is the missing number?
    20 + ? = 70

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