Barrons AP Calculus - David Bock

AB 2. Let M = the temperature of the milk at time t. Then

The differential equation is separable:

where c = e −C.

Find c, using the fact that M = 40° when t = 0:

40 = 68−ce^0 means c = 28.

Find k, using the fact that M = 43° when t = 3:

Hence

Now find t when M = 60°:

Since the phone rang at t = 3, you have 30 min to solve the problem.