Subtraction strategies, part 2: Subtract in parts; subtract an easy number, then correct the answer
Besides using the basic subtraction facts, here is another strategy for subtracting a single-digit or two-digit number from a two-digit number: subtract in parts.
For example, to subtract 52 − 5, first subtract enough that you go "down" to the previous ten, or to 50. That means we subtract 52 − 2. Then we still need to subtract 3 more. So, we go 50 − 3 = 47.
The next strategy is this. Instead of subtracting 29 from 66, we can subtract 30 (an easy number). It makes for a much easier problem to solve! Lastly, we adjust the answer, because in subtracting 30 instead of 29, we subtracted one too much. This is a really neat strategy and works for many kinds of problems, such as 99 + 87 or 4031 − 999.
See also
Subtraction strategies, part 1
Math Mammoth Grade 3 curriculum