Question 335060: John drives from Town A to Town B , a distance of 720 km , at a constant speed. When he returns from Town B to A, he saves an hour of travel time by increasing his average speed by 10 km/h. find the total time taken for the whole journey(to and fro)
Answer by stanbon(75887)   (Show Source):
You can put this solution on YOUR website! John drives from Town A to Town B , a distance of 720 km , at a constant speed.
distance = 720 km ; rate = x km/h ; time = 720/x hrs.
-------------------------------------------------------------
When he returns from Town B to A, he saves an hour of travel time by increasing his average speed by 10 km/h.
distance = 720 km ; rate = (x+10) km/h ; time = 720/(
Find the total time taken for the whole journey(to and fro)
Equation:
time to - time from = 1 hr
720/x - 720/(x+10) = 1
---
Multiply thru by x(x+10) to get:
720(x+10) - 720x = x(x+10)
7200 = x^2+10x
x^2+10x-7200 = 0
(x+90)(x-80) = 0
---
x = 80 km/h ; time to = 720/80 = 9 hrs.
-----
x+10 = 90 km/h ; time from = 720/90 = 8 hrs.
---
Total time = 9+8 = 17 hrs.
==================
Cheers,
Stan H.
==============
|
|
|
