Problem 3:

Two cars are traveling at 60 mph and 50 mph, respectively, according to a pedestrian. When they collide, their approaching speed will be

(a)  110 mph.
(b)  between 50 mph and 60 mph.
(c)  between 10 mph and 110 mph.
(d)  between 0 mph and 60 mph.
 

Answer