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December 22, 2014

Bird flying in a square

People A,B,C,D, each is at each edge of a square, the square side is 100 meter. A moves to B, B moves to C, C moves to D, D moves to A at speed 1m/s. Simultaneously a bird flies from A to B, then to C, then to D, then to A and so on. The bird meets D for the first time at the 30 second, when will it meet D for the third time?