IBPS PO Mains 2017 Paper for online practice

Two trains, 100 km apart, travel towards each other on the same track. One train travels at 40 km/hr; the other travels at 60 km/hr. A bird starts flying at a speed of 90 km/hr, at the same location of the faster train. When it reaches the slower train, it turns around and flies in the opposite direction at the same speed. When it reaches the faster train, again it turns around and so on. When the two trains collide, how far has the bird flown?