Estimate Smarter: Divide and Subtract
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Estimate Smarter: Divide and Subtract
Year 5 Mathematics ACARA v9 Curriculum 45 minutes
WALT - We Are Learning To
Estimate answers using division strategies Estimate answers using subtraction strategies Choose the best estimation method for different problems Check if our estimates are reasonable
Success Criteria - How We Know We've Succeeded
I can round numbers to make division easier I can use friendly numbers for subtraction I can explain which estimation strategy works best I can check if my estimate makes sense I can solve real-world problems using estimation
Why Do We Estimate?
Estimation helps us solve problems quickly and check if our answers make sense!
I Do - Teacher Modelling: Division Estimation
Problem: 847 ÷ 9 Step 1: Round 847 to 900 (friendly number) Step 2: 900 ÷ 9 = 100 Step 3: Check - does 100 seem reasonable? Actual answer: 94.1... so our estimate was close!
I Do - Teacher Modelling: Subtraction Estimation
Problem: 623 - 287 Step 1: Round 623 to 600, round 287 to 300 Step 2: 600 - 300 = 300 Step 3: Check - does 300 seem reasonable? Actual answer: 336, so our estimate was close!
We Do - Guided Practice Together
Let's try together: 456 ÷ 7 What friendly numbers should we use? 456 becomes... ? 7 stays as 7 So our estimate is... ?
Estimation Strategies Comparison
{"left":"Division: Round to numbers that divide easily\nUse multiples of 10, 100, or 1000\nKeep divisor simple when possible","right":"Subtraction: Round both numbers to friendly numbers\nUse numbers ending in 0 or 5\nMake mental math easier"}
Think and Discuss
Which is a better estimate for 789 ÷ 8? A) 800 ÷ 8 = 100 B) 790 ÷ 10 = 79 Turn to your partner and explain your thinking!
You Do - Independent Practice
Solve these estimation problems: 1) 543 ÷ 6 ≈ ? 2) 892 - 456 ≈ ? 3) 1,247 ÷ 9 ≈ ? 4) 734 - 298 ≈ ? Show your rounding steps!
Differentiation Support
Support: Use number lines and hundreds charts Support: Start with smaller numbers (2-digit) Core: Practice with 3-digit numbers Extension: Try 4-digit numbers and mixed operations Extension: Create your own estimation problems
Real-World Application
Shopping scenario: You have $50 to spend Items cost: $12, $18, $7, $9 Estimate: Can you buy all items? Use estimation to check before calculating exactly!