Unit 3 – Addition and subtraction
Subtraction with 3-digit numbers
1 We can complete the subtraction 689 − 336 using different methods. Will the actual answer be more or less than the estimate 700 − 300 = 400? 689 − 336 = 600 − 300 = 300 80 − 30 = 50 9 − 6 = 3 300 + 50 + 3 = 353 353 –300 –6 –30 689 389
359 What is the same and what is different about the methods? What calculation can you use to check?
689 − 336 = 689 − 300 − 30 − 6 = 389 − 30 − 6 = 359 − 6 = 353
2 We can also solve subtractions using the written column method.
We start by subtracting the ones: 9 ones − 6 ones = 3 ones 8 tens − 3 tens = 5 tens 6 hundreds − 3 hundreds = 3 hundreds
H
T O
H T O 6 8 9 − 3 3 6 3 5 3
– 3
3
6
Which method did you prefer for this calculation? Why?
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04/05/2022 15:49
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