Mental Math Strategies

Subtraction by counting tens

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). Since counting by tens comes easily to many students, we will count up by tens as part of a strategy for mental subtraction.


Step by step | Subtraction by counting tens

  1. Count up from the smaller number by tens.
  2. Stop counting as close to the larger number as possible, without going over. Remember this count.
  3. Count on to the larger number. Add this count to the first count to find the total difference.

Example | Subtraction by counting tens

Q: 48 − 26

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A: The difference of 48 and 26 can be found by counting up from 26 to 48. Beginning at 26, we first count by tens up to 46, a count of 20. Counting on to 48 yields 2 more, which we add to the count to find the total difference:
20 + 2 = 22.

Practice | Subtraction by counting tens