MathIsimple
Lesson 2-4

Subtraction Strategies

Master subtraction strategies including decomposition and inverse operations

Multiple StrategiesInverse OperationsVisual ToolsProblem Solving
Start LearningBack to Unit 2

Key Strategies

Master different approaches to solve subtraction problems

Decomposition Strategy

Break down the larger number into 10 and some more, then subtract from 10 first, then add the remaining amount.

Examples:

14 - 6: Break 14 into 10 + 4, subtract 6 from 10 = 4, add 4 = 8
16 - 9: Break 16 into 10 + 6, subtract 9 from 10 = 1, add 6 = 7
13 - 5: Break 13 into 10 + 3, subtract 5 from 10 = 5, add 3 = 8

Inverse Operations

Think of subtraction as the opposite of addition. Ask 'what number plus the smaller number equals the larger number?'

Examples:

11 - 8: Think '8 + ? = 11', answer is 3
15 - 7: Think '7 + ? = 15', answer is 8
12 - 4: Think '4 + ? = 12', answer is 8

Strategy Selection

Choose the best strategy based on the numbers. Use inverse operations for simple problems, decomposition for harder ones.

Examples:

12 - 3: Use inverse operations (3 + 9 = 12)
16 - 9: Use decomposition (16 = 10 + 6, 10 - 9 = 1, 1 + 6 = 7)
14 - 7: Use inverse operations (7 + 7 = 14)

Interactive Practice

Practice different subtraction strategies with interactive tools

Strategy Practice

Practice choosing and using different subtraction strategies.

Activity: Select the best strategy and solve subtraction problems

Decomposition Tool

Use visual tools to practice the decomposition strategy.

Activity: Break numbers apart and subtract step by step

Inverse Operations Game

Practice thinking of subtraction as the opposite of addition.

Activity: Find the missing number in addition facts to solve subtraction

Example Library

See step-by-step solutions using different subtraction strategies

14 - 6 using Decomposition

Problem:

Use the decomposition strategy to solve 14 - 6

Solution:

14 - 6 = 8

Steps:

  1. 1Break 14 into 10 + 4
  2. 2Subtract 6 from 10: 10 - 6 = 4
  3. 3Add the remaining 4: 4 + 4 = 8
  4. 4So 14 - 6 = 8

Visual:

14 circles = 10 circles + 4 circles, take away 6 from the 10, leave 4 + 4 = 8

11 - 8 using Inverse Operations

Problem:

Use inverse operations to solve 11 - 8

Solution:

11 - 8 = 3

Steps:

  1. 1Think: What number plus 8 equals 11?
  2. 2Ask: 8 + ? = 11
  3. 3The answer is 3 because 8 + 3 = 11
  4. 4So 11 - 8 = 3

Visual:

8 circles + 3 circles = 11 circles, so 11 - 8 = 3

16 - 9 using Decomposition

Problem:

Use the decomposition strategy to solve 16 - 9

Solution:

16 - 9 = 7

Steps:

  1. 1Break 16 into 10 + 6
  2. 2Subtract 9 from 10: 10 - 9 = 1
  3. 3Add the remaining 6: 1 + 6 = 7
  4. 4So 16 - 9 = 7

Visual:

16 circles = 10 circles + 6 circles, take away 9 from the 10, leave 1 + 6 = 7

15 - 7 using Inverse Operations

Problem:

Use inverse operations to solve 15 - 7

Solution:

15 - 7 = 8

Steps:

  1. 1Think: What number plus 7 equals 15?
  2. 2Ask: 7 + ? = 15
  3. 3The answer is 8 because 7 + 8 = 15
  4. 4So 15 - 7 = 8

Visual:

7 circles + 8 circles = 15 circles, so 15 - 7 = 8

Congratulations!

You've completed Unit 2: Addition & Subtraction within 20! You now know multiple strategies for solving addition and subtraction problems.

View All UnitsLearning Hub
Previous Lesson
Unit 2 Complete!
View All Units