Mental subtraction strategy: think of the difference between the numbers

We look at several subtraction problems (2-digit and 3-digit) where the most effective strategy is to think of the difference between the numbers. This strategy works best when the numbers to be subtracted are close to each other.
The last example we look at is the two-digit subtraction 72 - 37. I solve it by finding the difference between 37 and 72 -- essentially "adding up" from 37 to 72, in three different parts. I show arrows with jumps -- like using a number line without tick marks.
Practice two-digit mental math with these free online exercises:
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Play Hidden Picture Game and practice mental subtraction:
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This lesson is part of the Math Mammoth Grade 3 Curriculum:
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