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:: The Fly and the Cyclists ::

Two cyclists 20 km apart start at the same instant and ride towards each other along a straight road at a speed of 10 km/h. At the same instant a fly on the forehead of one of the riders starts to fly at 15 km/h towards the other rider, alights on his forehead and then flies back to the first rider.

The fly travels back and forth over the continuously decreasing distance between the two riders until it is finally squashed as the foreheads of the two riders meet. How far has the fly flown when all his journeys are added together?

Answer