Some stories are about a group that changes: things are added to it or taken from it. Use your facts within 20.
| What is missing? | Story | Number sentence |
|---|---|---|
| the end | had 8, got 4 more | $8 + 4 = \square$ |
| the change | had 8, got some, now has 12 | $8 + \square = 12$ |
| the start | had some, got 4, now has 12 | $\square + 4 = 12$ |
Key idea
Write the story as a number sentence, with a box for the number you don’t know. Then find the box.
Why it works
The number sentence follows the story in order: start, change, end. So you can see which number is missing.
Worked example: How many more?
Ben had 8 stickers. He got some more. Now he has 12. How many did he get?
- Story: $8 + \square = 12$.
- From 8 up to 12 is 4.
- Ben got 4 stickers.
Answer: 4
Worked example: How many at first?
Some birds sat on a wire. 5 flew away. Now 7 are left. How many birds were there at first?
- Story: $\square - 5 = 7$.
- Put the 5 back: $7 + 5 = 12$.
- There were 12 birds.
Answer: 12
For grown-ups: Ask your child to act out the story with small toys before solving. Then ask, “Which number did we not know?”