A car drives downhill with the speed of 90 m/h. On a level road, the same car goes 72 m/h, and uphill it goes "only" 60 m/h.

It takes this car 5 hours to go from town A to town B. The return trip only takes 4 hours.

Find the distance between the two towns.

x/60 + y/72 + z/90 = 5 and
x/90 + y/72 + z/60 = 4
multiply each equation by 360:
6x + 5y + 4z = 1800 and
4x + 5y + 6z = 1440
Add these two equations:
10x + 10y + 10z = 3240
Divide by 10:
x + y + z = 324

Posted by Charlie on 2003-02-10 02:50:33