Paul went on a bike ride of 72 miles. He realized that if he had gone 15 mph faster, he would have arrived 20 hours sooner. How fast did he actually ride?

Question

Paul went on a bike ride of 72 miles. He realized that if he had gone 15 mph faster, he would have arrived 20 hours sooner. How fast did he actually ride?

Answer 1

Since d = rt and the distances are the same...

 

rt = (r + 15)(t - 20)

rt = rt + 15t - 20r - 300

15t - 20r = 300

 

Let's find two factors of 72 for which this works.

 

t has to be larger than 20 in order to subtract from 2t and get 300.

 

15(24) - 20(3) = 360 - 60 = 300

 

He rode 3 mph.