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A cup of coffee co ols from 90°C to 80°C in t minutes when the room temperature is 20°C. The time taken by the similar cup of coffee to cool from 80°C to 60°C at the same room temperature is :

1. 5 13 t
2. 13 10 t
3. 10 13 t
4. 13 5 t

Correct answer: 5 13 t

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