Question 340525: two cyclist,20 miles apart,start at the same instant and ride towards each other along a straight road at a speed of 10 miles per hour. at the same instant a fly on the forehead ofone of the riders starts to fly at 15 mile per hour toward the other rider, alights on his forehead, and the immediately flies back to the first rider. the fly travels back and forth over the continously decreasing distance between the two riders until the two riders meet. how far has the fly flown when all its journeys are added together.
Answer by galactus(183)   (Show Source):
You can put this solution on YOUR website! The fly take off toward the opposite cyclist, but at the same time the cyclist is coming toward the fly.
This means we have 15t+10t=20.
25t=20
t=4/5 hrs or 48 minutes the fly has flown and the cyclist has pedaled.
In this time the fly flew 12 km and each cyclist traveled 8 km. 15(4/5)=12.
Since the cylists are pedaling 10 kph toward each other, in 1 hour they will meet.
But as the fly heads back to the other cyclist, the cyclist is heading toward him at 10 km/hr.
There is 4 km left to cover as the fly heads back to the cyclist it started out on.
In 12 minutes the fly covers 15(1/5)=3 km
Thus, the fly covers 12+3=15 km altogether.
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