Problema Solution
Chris and Leslie drove as total of 969 miles in 17.4 hours. Chris drove the first part of the trip and averaged 45 miles per hour. Leslie drove the remainder of the trip and averaged 65 miles per hour. For what length of the time did Chris drive?
Answer provided by our tutors
let
v1 = 45 mph the avg. speed of Chris
t1 = the time that Chris drove
v2 = 65 mph the avg. speed of Leslie
t2 = the time that Leslie drove
since avg. speed = distance/time => distance = speed*time
the total distance is 969 mi
v1*t1 + v2*t2 = 969
45t1 + 65t2 = 969
the total time is 17.4 hours
t1 + t2 = 17.4
by solving the system of equations
45t1 + 65t2 = 969
t1 + t2 = 17.4
we find
t1 = 8.1 hr
t2 = 9.3 hr
click here to see the step by step solution of the system of equations
t1 = 8.1 hr = 8 hr 0.1*60 min = 8 hr 6 min
Chris drove for 8 hours and 6 minutes.