A man completed a trip of 136 km in 8 hrs. Some part of the trip was covered at 15 km/hr. What is the part of the trip covered at 18 km/hr?
distance at 15 km/h --- x
distance at 18 km/h ---- 136-x
x/15 + (136-x)/18 = 8
multimply each term by 90
6x + 5(136-x) = 720
6x + 680 - 5x = 720
x = 40
distance at 15 km/h is 40 km
distance at 18 km/h is 136-40 or 96 km
check:
40/15 = 2 2/3 hrs
96/18 = 5 1/3 hrs , for a total of 8 hrs.