Advanced MathHardHalving time for a cooling cup
Advanced Math practice question
The amount by which a cup of coffee's temperature exceeds room temperature halves every 10 minutes. If the excess is 80°C now, after how many minutes will the excess be 10°C?
Answer: 30
80 → 40 → 20 → 10 is three halvings, or 30 minutes.
Common wrong answers
- If you answered 8
- 8 is 80 ÷ 10.
- If you answered 40
- 40 is four halvings, reaching 5°C.
- If you answered 70
- 70 subtracts 10 from 80 as if the excess fell by 10 each period.
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