Addition & Subtraction Mental Strategies
Year 5 Mathematics Developing fluency with mental calculations Building number sense and confidence
WALT - Week Overview
We Are Learning To develop fluency with addition and subtraction We Are Learning To use mental and written strategies effectively We Are Learning To understand the inverse relationship between operations We Are Learning To adjust numbers to make calculations easier
Success Criteria - What We'll Achieve
I can recall basic addition and subtraction facts quickly I can solve problems using mental and written strategies I can adjust numbers to make calculations easier I can use inverse relationships to check answers I can find missing numbers in equations I can add and subtract decimals (up to two decimal places)
DAY 1: Learning Intentions
WALT develop fluency with basic addition and subtraction facts WALT use mental strategies for simple calculations WALT understand what makes calculations easier
Warm-Up: Number Bond Race
Work in pairs Race to find number bonds to 10, 20, and 100 Use Numicon shapes if needed Record your fastest times
Mental Strategy 1: Counting On
Start with the larger number Count on the smaller amount Example: 47 + 6 = start at 47, count 48, 49, 50, 51, 52, 53 Most efficient for adding small numbers
Practice: Counting On
Try these problems using counting on: 38 + 5 = 72 + 8 = 156 + 7 = Extension: 2.3 + 0.6 =
Mental Strategy 2: Making 10
Break apart numbers to make friendly numbers Example: 8 + 5 = 8 + 2 + 3 = 10 + 3 = 13 Example: 27 + 6 = 27 + 3 + 3 = 30 + 3 = 33 Makes calculations much easier!
Think-Pair-Share
How could you use 'making 10' to solve 39 + 7? Discuss with your partner Be ready to share your thinking
DAY 2: Learning Intentions
WALT use compensation strategies for addition and subtraction WALT adjust numbers to make calculations easier WALT check our work using inverse relationships
Mental Strategy 3: Compensation
Add or subtract a friendly number, then adjust Addition example: 48 + 19 = 48 + 20 - 1 = 68 - 1 = 67 Subtraction example: 75 - 19 = 75 - 20 + 1 = 55 + 1 = 56 Very powerful for numbers ending in 8, 9, or 1, 2
Compensation Challenge
Solve using compensation strategy: 56 + 29 = 83 - 18 = 147 + 39 = Extension: Create your own compensation problem
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