Mental Math Strategies

Subtraction by counting up

Practice Table of Contents

Introduction

Subtraction can be carried out in two ways: by taking away (begin with 8 and take away 5) or by counting up (begin with 5 and count up to 8). Counting up is more like addition and may be easier for some students. We will use this "counting up" method as part of a strategy for mental subtraction.


Step by step | Subtraction by counting up

  1. Count up from the smaller number to the next ten. Remember this count.
  2. Count up from this ten to the larger number.
  3. Add this count to the first count to find the total difference.

Example | Subtraction by counting up

Q: 34 − 18

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A: The difference of 34 and 18 can be found by counting up from 18 to 34. Beginning at 18, we first count up to 20, a count of 2. Next, we count up from 20 to 34, a count of 14. Lastly, we combine our counts: 2 + 14 = 16.

Practice | Subtraction by counting up