Topic 4 of 8
Adding and subtracting within 10
Step 2 · Numbers to 100 topics
Adding puts groups together; subtracting takes some away. Solve both, and story problems, with numbers up to 10.
Adding is putting together
Adding means putting groups together to find how many in all. 3 red balls and 2 blue balls make 5 balls.
- red balls
- blue balls
We write it 3 + 2 = 5. The + sign means add, or plus. The = sign means is the same as.
To add, count all the things, or count on: start at 3 and count 2 more, four, five.
You can add in either order: 3 + 2 and 2 + 3 both make 5.
Subtracting is taking away
Subtracting means taking some away to find how many are left. 7 birds sit on a fence and 3 fly away. 4 birds are left.
- birds left
- flew away
We write it 7 − 3 = 4. The − sign means take away, or minus.
To subtract, take away and count what is left, or count back: start at 7 and count back 3, six, five, four.
Story problems
A story problem tells a story with numbers. Ask: are things being put together, or taken away?
Example: Putting together
Ana has 6 shells. She finds 3 more. How many shells does she have now?
- She finds more, so things are put together: add.
- 6 + 3: count on from 6: seven, eight, nine.
Answer9 shells
Example: Taking away
There are 8 grapes. Leo eats 5. How many grapes are left?
- Some grapes are eaten, so things are taken away: subtract.
- 8 − 5: count back from 8: seven, six, five, four, three.
Answer3 grapes
Try it yourself
Work each one on paper first, then open the answer to check.
4 + 3
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7. Count on from 4: five, six, seven.
9 − 2
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7. Count back from 9: eight, seven.
5 + 5
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10.
There are 6 ducks. 4 swim away. How many are left?
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2 ducks, because 6 − 4 = 2.
You have 2 stickers and get 6 more. How many now?
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8 stickers, because 2 + 6 = 8.
7 − 0
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7. Taking away nothing leaves all 7.