You have just made a cup of black coffee with boiling water (Tb = 100^oC) and are about to pour in some milk (Tm = 5^oC). However you will not be drinking the coffee for several minutes (2 minutes) as you have just been called to the telephone. The temperature of the room is 20^oC.

1. In order to have the hottest cup of white coffee is it better to add the milk to the coffee now or when you return from the telephone ? In either case assume that the milk to be added is at 5^oC and that it will be stirred into the coffee. Please explain your answer.

2. Please draw two graphs for the above situations. One where the milk is added immediately and the other when the milk is added after two minutes. Draw the graph for the first three minutes. (PTO)

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