By rounding each number in the calculation correct to 1 significant figure, estimate the value of:
\( \frac{38.7 \times 3.115}{20.3 – 4.1^2} \)
You must show all your working.
▶️ Answer/Explanation
Ans: 30
1. Round numbers: 38.7→40, 3.115→3, 20.3→20, 4.1→4
2. Calculate denominator: 20 – 4² = 20 – 16 = 4
3. Calculate numerator: 40 × 3 = 120
4. Divide: 120 ÷ 4 = 30
Sophie buys 73 books for her school. Each book costs $21.95 .
(a) By rounding each number correct to 1 significant figure, estimate the total cost of these books.
(b) Write down whether this estimate is greater or less than the exact cost. Explain how you decide, without working out the exact cost.
▶️ Answer/Explanation
Ans:
(a) 70 × 20 = $1400 (73 → 70, 21.95 → 20)
(b) Less than because both numbers were rounded down (70 < 73 and 20 < 21.95)