Question 33851
Assume that x mph be the speed the dad should be driving to catch the boy in 15 minutes; 15 minutes = 1/4 hour
If the dad drives x miles in 1 hour, he would drive x/4 miles in 15 minutes.
By the time the dad catches his boy, the boy would travel for 1 and 1/4 hours by bike.  Riding at 8 mph, the boy would travel 8+2=10 miles;
The distance for both the dad and boy must be the same for the dad to overatke his boy.
So, x/4 = 10
=> x = 40
Answer: Dad has to drive at 40 mph.