Completing a ten in mental addition
Making one addend a multiple of ten can simplify mental calculation. Track the amount taken from the other number so the total stays unchanged.
Try it yourself first.
Solve 38 + 17 by first making 38 into 40. Clearly show what remains of 17.
View the solution or example answer
Move two from 17 to 38: 40 + 15 = 55. The total is preserved. Changing 38 to 40 while keeping 17 would increase it by two.
Your next step.
Check using another method. Explain the strategy accurately before focusing on speed. Split the same total into different pairs to see the balance.
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