John Runs the Same Three-Mile Route Every Day

Multiple Choice

John runs the same three-mile route every day. If he takes his dog, it adds 25 seconds to his running time. If it is cold, it adds 10 seconds to his running time. Suppose he ran one cold morning with his dog. What change in his time would represent no interaction between the two variables (dog and temperature) ?

A) increase 10 seconds
B) increase 25 seconds
C) increase 35 seconds
D) decrease 15 seconds
E) none of the other alternatives are correct.