Puzzle - A Bird and Two Trains

Puzzle

Consider two trains starting from two points X and Y respectively. Trains which starts from X travels at 15 Km/hr while the train which starts from Y travels at 20 Km/hr. Both trains start at the same time. A Bird also start from X at the same time. The speed of the Bird is 25 Km/hr. The Bird flies from X to Y until it meets the train started from Y. After that it changes its direction and fly towards the train started from X. When it meets X it start flying toward Y and so on until the train meets. What is the total distance covered by the bird ?


Hint : Think Simple !

Solution

Answer is too simple . It involves only the basic time - distance formula.

The Speed of the Bird is constant. Only we need to calculate time until which it flies. The bird flies until two trains meet each other,

Total Time  === Time taken by the two trains to meet each other

Assume the initial distance between two trains is d.

Time taken  by the trains to collide is d / (20 + 15).

Distance traveled by the bird is 25 * ( d / 35 ) = ( 5 / 7 ) * d.