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A body cools from 65 deg C to 60 deg C in 5 minutes and from 60 deg C to 55 deg C in 7 minutes. Find the room temperature and the time taken to cool from 55 deg C to 50 deg C.

1. 40 deg C, 10 min
2. 35 deg C, 11.67 min
3. 45 deg C, 11.67 min
4. 40 deg C, 15 min

Correct answer: 45 deg C, 11.67 min

Solution

Dividing the two cooling equations gives room temperature 45 deg C, and the third interval then takes 11.67 minutes.

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