Unit 4 Contents

Using Mental Math to Subtract

11. Talk with a partner about the following subtraction problems. Discuss which problems are easy and which are hard. Which would you solve with mental math and which would you solve with paper and pencil?
1. 101 − 2
2. 238 − 72
3. 3004 − 2999
4. 375 − 125
5. 54 − 34
6. 602 − 593
7. 487 − 256
8. 381 − 200
9. 52 − 25
10. 150 − 30
11. 91 − 21
12. 826 − 487
12. Choose two problems from Question 11. Be prepared to tell the class how you would solve them mentally.

Mrs. Dewey's class talked about how they solved the problem 75 − 38 using mental math. Some students counted back and other students counted up.

Counting Back to Solve 75 − 38:

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