Saving Estimation Reasonableness Assessment

Name:

Date:

Calculator and savings chart illustration

🎯 WALT: We Are Learning To

Determine whether an answer is reasonable by using properties of operations, estimation and the context of the problem

Success Criteria:

• I can estimate timeframes for saving goals

• I can evaluate if savings calculations are reasonable

• I can convert between fortnights, months and years

📊 Part 1: Multiple Choice Questions

1. Sarah saves $200 each fortnight. To estimate how long it would take to save $10,000, which calculation is most reasonable?

$10,000 ÷ $200 = 50 fortnights (about 2 years)

$10,000 ÷ $200 = 50 weeks (about 1 year)

$10,000 ÷ $400 = 25 months (about 2 years)

$10,000 ÷ $100 = 100 fortnights (about 4 years)

2. If someone estimates "it would take one month less than two years to save $10,000 by saving $200 each fortnight", is this estimate reasonable?

Yes, because 50 fortnights equals about 23 months

No, because it would take exactly 2 years

No, because it would take 3 years

Yes, but only if you save $400 per fortnight

3. Tom calculates he needs 48 fortnights to save $9,600 at $200 per fortnight. To check if this is reasonable, which estimation strategy is best?

Round to: 50 × $200 = $10,000 ✓ Reasonable

Convert to: 48 weeks × $200 = $9,600 ✓ Reasonable

Estimate: $9,600 ÷ 48 = $200 per month

Calculate: 48 ÷ 26 = less than 2 years

🧠 Part 2: Show Your Thinking

4. Foundation Level: Complete this estimation: If I save $200 every fortnight, in one year (26 fortnights) I will save approximately $______.

5. Standard Level: Explain why the estimate "one month less than two years" is reasonable for saving $10,000 at $200 per fortnight. Show your working.

6. Extension Challenge: If someone wants to save $15,000 in exactly 18 months, estimate how much they need to save per fortnight. Is $350 per fortnight a reasonable amount? Justify your answer.

Differentiation Support: Use 26 fortnights = 1 year, 52 fortnights = 2 years