The jogging fly
Just like every other morning, two friends living apart start jogging towards each other. At the same time, a fly on the head of one of the joggers also starts flying towards the other, back and forth, until the friends meet.
What is the distance flown by the fly in kilometres if both of the friends jog at a velocity of and the fly flies at the velocity of
The answer is 10.
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1 solution
In a fascinating book, T i m e t r a v e l a n d O t h e r M a t h B e w i l d e r m e n t s , Martin Gardner tells the story of a Hungarian mathematician, John von Neumann who was asked to solve this problem at a celebration. Neumann gave the answer almost instantly disappointing the asker. The answer he gave was very simple. Given the velocities of the friends, and the distance between them, it's easy to say that it'll take one hour for them to meet. Given that the fly crosses 10 h k m , it's easy to say that the distance the fly flew is 10 km