Two trains, 200 kilometres apart, are moving towards each other, each going at a speed of 50 kmph.
A crazy fly, starting on the front end on one of the trains flies back and forth between them at the rate of 75 kmph. It touches one train returns to the other and flies back, doing this continuously till the trains collide, crushing the insect.
What is the total distance the fly travelled before it got crushed?
The answer can be worked out in a jiffy, without using pen and paper.