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        riddles >> easy >> Car journey
        
(Message started by: NickH on Feb 27^th, 2004, 1:45pm)

Title: Car journey
Post by NickH on Feb 27^th, 2004, 1:45pm

A car travels downhill at 72 m.p.h. (miles per hour), on the level at 63 m.p.h., and uphill at only 56 m.p.h. The car takes 4 hours to travel from town A to town B. The return trip takes 4 hours and 40 minutes.

Find the distance between the two towns.

Title: Re: Car journey
Post by John_Gaughan on Feb 27^th, 2004, 9:15pm

The distance is [hide]273[/hide] miles.

:: [hide]Since d = rt, and d is the same for both uphill and downhill, set r₁t₁ = r₂t₂, where r₁ is 72 mph, t₁ is t, r₂ is 56 mph, and t₂ is t + 2/3, since the 40 minute time difference is equal to 2/3 of an hour (mind the units). From there you get the time spent driving at 72 mph. Algebra gives the time spent driving at 63 mph based on the total time, and so on. Then take the rate times the time to get the distance.[/hide] ::

It is important to note that where during the trip you encounter hills is irrelevant. The only important thing is to know the total time spent driving up or down hill.