The change in temperature of object is proportional to the difference between the object's temperature and the surrounding medium's temperature. A liquid, with an initial temperature of 200 degrees F, is placed in a room with an air temperature of 78 degrees F at 10:00AM. At 10:15 AM the liquid's temperature was 140 degrees F. At what time of day will the liquid measure at a temperature of 80 degress F? Set up and solve the differential equation.
A simple, step-by-step guide for converting these kinds of word problems to differential equations would be a nice addition to the steps used to set it up and solve it.