Question Video: Subtracting within 100 Using Compensation Mathematics • 2nd Grade

James knows a way to make finding 44 − 17 easier. What is 47 − 20? What is 44 − 17?

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Video Transcript

James knows a way to make finding 44 take away 17 easier. He says, if I add 13 to both numbers, the difference stays the same; I can find 44 take away 20 instead. What is 47 take away 20? What is 44 takeaway 17?

James needs to calculate 44 take away 17. He adds three to 44. So he now has 47 and he adds three to 17 which gives him 20. We need to calculate 44 take away 17 and 47 take away 20. 47 has four tens and seven ones. And we need to take away 20 or two tens. Seven ones take away no ones leaves us with seven ones. And four tens take away two tens leaves us with two tens. 47 take away 20 is 27. This means that 44 take away 17 also equals 27. We know this because if James adds three to both numbers, the difference stays the same. 44 take away 17 equals 27. 47 take away 20 equals 27. The difference stays the same.

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