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

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?

Try the free Mathway calculator and problem solver below to practice various math topics. Try the given examples, or type in your own problem and check your answer with the step-by-step explanations.