1. The problem statement, all variables and given/known data The circumference of a circle is increasing by 4 inches per second. What is the rate of change of the diameter with respect to time if the radius is 2 inches? 2. Relevant equations C = 2∏r = ∏d. 3. The attempt at a solution dC/dt = 4 = ∏dd/dt. dd/dt = 4/∏ Is this it? It seems as if the information given about the radius is irrelevant.