Counting Back Strategy

Arithmetic · Axiom Academy

A mental math technique for subtraction — start at the first number and count backward by the amount you take away. To subtract, start at the first number and count back. Take 9 − 3 : begin at 9 and step back three times — 8, 7, 6 . The number you land on, 6 , is the answer. Each hop is one step to the left (−1) Every count-back follows the same three moves. The animation applies them to 8 − 3 . Start at 8, count back three: 7, 6, 5 . The landing number 5 is exactly 8 − 3 . The same idea works for any small count back. Watch 12 − 4 on the number line, then check the worked examples below. You've seen how subtraction can be done in your head by stepping backward along the number line. Scroll up to revisit any step.

This is the written version of the interactive lesson above. See the full Arithmetic course.