Lesson Plan

Subtracting Mixed Numbers Using the Decomposition Strategy

Teach your students to subtract mixed numbers with like denominators using the strategy of decomposition. This strategy helps students to manipulate and break down numbers to help them solve tricky subtraction problems.
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Need extra help for EL students? Try the Writing Questions for Word Problems pre-lesson.
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Need extra help for EL students? Try the Writing Questions for Word Problems pre-lesson.

Learning Objectives

Students will be able to solve subtraction problems with mixed numbers that have like denominators using the decomposition strategy.

The adjustment to the whole group lesson is a modification to differentiate for children who are English learners.
EL adjustments

Introduction

(5 minutes)
  • Write on the board: 43 – 17 = ?
  • Ask your students to explain how they would solve this problem. (Possible answers: adding on from 17 to 43 or regrouping one ten from the 43 into ten ones and then subtracting.)
  • Explain that just like there is more than one strategy for subtracting whole numbers, there is more than one strategy for subtracting mixed numbers (a number that has a part that is a whole and a part that is a fraction).
  • Tell students that today you are going to teach them to decompose, or break numbers apart when subtracting mixed numbers.

Beginning

  • Give students the opportunity to talk with a partner regarding their strategy to solve the subtraction problem before sharing with the whole group.

Intermediate

  • Provide visuals and examples to demonstrate the meaning of the words "decompose," "strategy," and "mixed numbers."
  • Have students repeat or rephrase the definition of the key vocabulary terms in the lesson.