CACMath

Lesson 7 of 8 · Grade 1

Find the missing number

To solve 4 + ? = 9, ask: how many more to get from 4 to 9?

Bea, a pink bunny, holding up one paw to count

Step 1

Learn it

  1. A box for the unknown

    4 + ? = 9. The ? is the number we need.

  2. 0 1 2 3 4 5 6 7 8 9 10

    Count on to the whole

    Start at 4. Hop to 9. That is 5 hops.

  3. Check it

    4 + 5 = 9. Yes. The missing number is 5.

Step 2

Watch how

Two examples, worked out one step at a time.

  1. 0 1 2 3 4 5 6 7 8 9 10

    4 + ? = 9

    Hop from 4 up to 9: 5 hops. Or 9 − 4 = 5. Check: 4 + 5 = 9.

    Answer: 5

  2. ? + 6 = 11

    11 − 6 = 5. Check: 5 + 6 = 11.

    Answer: 5

Step 3

Play with it

Add blocks until both sides weigh the same.

Open the balance scale

Step 4

Practice

Five questions. Think first. Then tap Show answer.

  1. 3 + ? = 7

    Show answer

    4

  2. ? + 2 = 8

    Show answer

    6

  3. 6 + ? = 10

    Show answer

    4

  4. 5 + ? = 12

    Show answer

    7

  5. ? + 8 = 15

    Show answer

    7

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