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Decomposing 10: A Strategy for Subtraction

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Grade 1 Math | Lesson 4

Grade 1Common Core 1.OA.C.610 minutes

Learning Objectives

  • Understand the "decomposing 10" strategy for subtraction
  • Practice breaking down 10 to make subtraction easier
  • Apply the strategy to subtract numbers from 10 through 20

Introduction to the Decomposing 10 Strategy

The "decomposing 10" strategy is a powerful way to subtract numbers mentally. It works by breaking down the number 10 into smaller parts to make subtraction easier.

Why is this useful?

10 is a "friendly number" that makes mental math easier

It helps us subtract from larger numbers quickly

This strategy builds number sense and fluency

Example: 13 - 5

Using decomposing 10, we can break down 13 into 10 + 3

13−5
=
(10 + 3)−5

10 − 5 = 5, then 5 + 3 = 8

So, 13 − 5 = 8