Estimate Smart: Subtraction and Division Strategies
Year 5 Mathematics WALT: Use estimation strategies to check the reasonableness of subtraction and division calculations
Why Do We Estimate?
Helps us check if our answers make sense Saves time when we need quick answers Useful in real life - shopping, cooking, planning Like guessing jellybeans in a jar!
Let's Recap: Rounding Numbers
Round to nearest 10: 47 → 50 Round to nearest 100: 382 → 400 Look at the digit to the right 5 or more? Round up! Less than 5? Round down!
Group Challenge: Estimating Subtraction
Form groups of 4-5 students Each group gets subtraction problems like 482 - 179 Round both numbers to make it easier Use blocks or counters to help visualize Check your estimate with a calculator!
Estimating Division Made Easy
Round both numbers to make division simpler Example: 495 ÷ 9 becomes 500 ÷ 10 = 50 Use compatible numbers that divide easily Check: Does our estimate make sense?
Division Estimation Practice
Work in your groups Estimate division problems using rounding Use counters to model the division Record your estimates Check with calculators - how close were you?
Extension Challenge
Create your own real-life estimation problem Think about: shopping, cooking, sharing items Write the problem, estimate the answer Share with the class!
When Do We Estimate vs Calculate Exactly?
Estimate when: Planning a party, checking if you have enough money Calculate exactly when: Paying bills, measuring medicine Quick mental check: Does this answer seem right? Estimation helps us catch mistakes!
Success Criteria - Did We Achieve Our Goals?
✓ Round numbers to make estimation easier ✓ Use estimation to check if answers are reasonable ✓ Explain our estimation process clearly ✓ Work together respectfully in groups
Supporting All Learners
Visual aids: number lines and charts help everyone Hands-on materials make learning fun Work at your own pace with support Extension activities for those ready for more Everyone can succeed with estimation!
More Estimation slide decks
Other ready-to-teach decks on estimation.
