A thermometer is stored at 75 degrees. It is taken outside and reads 65 degrees after 5 minutes, and it reads 60 degrees after 10 minutes. Compute the temperature outside.

We use the equations from Newton’s law of cooling (example 3 on page 315 of Apostol). This gives us

We have since the outside temperature is constant, and we are given so , and . Therefore,

We are then given and so,

And,