Advanced MathMediumHalving repeatedly
Advanced Math practice question
A cup of tea cools so that the difference between its temperature and the room's temperature halves every 10 minutes. The difference is 60 degrees now. What will the difference be, in degrees, after 30 minutes?
Answer: 7.5 or 15/2
Three halvings in 30 minutes: 60 × (1/2)³ = 60/8 = 7.5.
Common wrong answers
- If you answered 15
- 15 is after two halvings (20 minutes).
- If you answered 20
- 20 divides 60 by 3, treating the process as linear.
- If you answered 30
- 30 is after ONE halving (10 minutes).
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