Decompose to Subtract

Solutions, examples, and videos to help Grade 2 students learn how to decompose to subtract from a ten when subtracting within 20 and apply to one-step word problems.

Common Core Standards: 2.OA.1, 2.OA.2

New York State Common Core Math Grade 2, Module 1, Lesson 5

NYS Math Module 1 Grade 2 Lesson 5

Using number bonds to decompose the ten and subtract from the tens. This is a mental math strategy that builds number sense and prepares students for problems with larger numbers.

Lesson 5 Concept Development

The focus of this activity is on solving problems with a common subtrahend (e.g., 11 – 8, 12 – 8, 13 – 8, etc.).
Next, students determine whether to subtract from the ten or the ones.

Lesson 5 Problem Set

1. Do we subtract from the tens or ones?
   11 - 2 =
   15 - 2 =
   16 - 4 =
2. Fill in the blank to make the number sentence correct.
   11 – 8 = 2 + ___
   16 – 9 = 1 + ___

Lesson 5 Concept Development
Explain how to decompose to subtract within 20
Lesson 5 Homework
3. Mrs. Jones bought 12 eggs from the store in the morning. Her husband brought home 5 more eggs in the evening. They used 8 of the eggs for dinner. How many eggs do they have left?
4. 11 pink roses and 7 red roses grew in Mrs. Thompson’s garden. She gave away 9 of the pink roses to her neighbor. How many roses does she have left?

EngageNY/Eureka Math Grade 2 Module 1 Lesson 5 Version 3
Make a ten to add within 100

1. Solve
   
2. Use the RDW process to solve.
   There were 28 students at recess. A group of 7 students came outside to join them. How many students are there now?

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