math help plz

Question

Jim began a 102 -mile bicycle trip to build up stamina for a triathlete competition. Unfortunately, his bicycle chain broke, so he finished the trip walking. The whole trip took 4 hours. If Jim walks at a rate of 3 miles per hour and rides at 39 miles per hour, find the amount of time he spent on the bicycle.
Jim rode for___________ hours.

Answer 1

Let x = the time on the bike.  Since the whole trip was 4 hours, the time walking is 4 - x

Then, since bike travel is at 39 mph and walking is at 3 mph, distance traveled is

39 x + 3(4 - x) = 102

39x + 12 - 3x = 102

36x = 90

x = 90/36 = 5/2 or 2.5

 

To check, 39*2.5 + 3*1.5 = 102