Mental subtraction strategy: use basic subtraction facts

We can solve 23 - 8 and 93 - 8 (and 63 - 8 etc.) by our knowledge of the basic subtraction fact that 13 - 8 = 5. Think of it this way: in 13 - 8, the answer goes "down" to the previous ten, and ends in 5. It works the same way for 63 - 8, for example: the answer is in the previous ten (in the 50s) and ends in 5.

The next part of this lesson is here (Subtract in parts):

Practice two-digit mental math with these free online exercises:

Play Hidden Picture Game and practice mental subtraction:

This lesson is part of the Math Mammoth Grade 3 Curriculum: