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A body takes 4 min. to cool from 61° C to 59° C. If the temperature of the surroundings is 30°C, the time taken by the body to cool from 51°C to 49° C is:

1. 4 min.
2. 3 min.
3. 8 min.
4. 6 min.

Correct answer: 6 min.

Solution

First: 2/4 = k(60-30) gives k=1/60. Second: 2/t = (1/60)(50-30) = 1/3, so t = 6 min (index 3).

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