Mathematics

Problem

A cup of tea is initially

90^{\circ}\text{C}

and cools to

60^{\circ}\text{C}

5

minutes in a

25^{\circ}\text{C}

room. Assuming the tea continues to cool according to

\displaystyle \frac{dT}{dt}=k\,(T-25)

with the same constant

k

, approximately how many minutes after it was first poured will the tea reach

40^{\circ}\text{C}

? a)

10\text{ minutes}

8\text{ minutes}

12\text{ minutes}

9\text{ minutes}