Some Snaps

some maths puzzles Courtesy: http://sds.podval.org/puzzles.html#ellipse-diagonal
Question: 2 pedestrians have one bike. They travel as follows: the first one rides the bike for some time, then drops it and continues walking in the same direction, while the second follows him by foot. Eventually, the second one finds the bike and rides it until he overtakes the first one. Then he gives the bike to the first one etc. Assuming that they walk with the same speed and bike faster than they walk, what is the speed of their travel?

Ans: The answer is: the harmonic average (the reciprocal of the arithmetic average of the reciprocals) of the walk and bike speeds. This is because both walk and bike equal distances.