Strategies for mental subtraction
These two videos explain various basic strategies we can use to mentally subtract two-digit numbers.
This first part covers two simple mental math strategies for subtracting a single-digit number from a two-digit number, such as 63 − 8 or 72 − 5.
The first strategy is to subtract in parts (or part-by-part). For example, think of 63 − 8 as 63 − 3 − 5. You first subtract 63 − 3 which is 60. Then you subtract the rest.
The second strategy is to use known subtraction facts. To solve 62 − 7 with this strategy means recalling 12 − 7 = 5. Then, the answer to 62 − 7 ends in 5, and is in the "previous ten", or in the fifties, thus it is 55!
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A few more mental math strategies for addition and subtraction of two-digit numbers. We also solve a puzzle with two unknowns. :)
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See also
Two-digit mental addition — online practice
Mental addition − add a 2-digit and a 1-digit number (with regrouping)
Number rainbow & fact families with 12
Math Mammoth Grade 2 curriculum
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