Unit 15 – The four operations
1 We can complete the subtraction 587 − 234 using different methods. Why is 600 − 200 = 400 a useful estimate?
What is the same and what is different about the methods? Where can you see subtracting a multiple of 100? Subtracting place value parts 587 − 234 = 500 − 200 = 300 80 − 30 = 50 7 − 4 = 3 300 + 50 + 3 = 353
− 200
− 4 − 30
353357
387
587
Subtracting back 587 − 234 = 587 − 200 − 30 − 4
= 387 − 30 − 4 = 357 − 4 = 353
2 What is different about the subtraction 587 − 239? Look at what happens when we try to subtract 9 ones.
1 1
10 10
1
10
1 1
1
100
10 10
1 1
100
10 10
1 1
1 1
100 100
10 10
1 1
100 100
10 10
1 1
1 1
100 100
10 10
1 1
100 100
10 10
1 1
1 1
5
8
7
5
7
17
We can complete the subtraction as: 587 − 239 = 500 − 200 = 300
70 − 30 = 40 17 − 9 = 8 300 + 40 + 8 = 348
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03/05/2022 10:20
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