Question

Two trains, 200 km apart, are moving toward each other at the speed of 50 km/hour each. A fly takes off from one train flying straight toward the other at the speed of 75 km/hour. Having reached the other train, the fly bounces off it and flies back to the first train. The fly repeats the trip until the trains collide and the bug is squashed.

What distance has the fly traveled until its death?

There is a complicated and an easy way to calculate this cool math puzzle.
Think outside the box.

Answer 1

if the fly is flying for 2 hours still at the same speed of 75 km/h then it flies a distance of 150 km

Answer 2

75 Km as in 1 hr the trains will collide

Answer 3

relative velocity of trains = 50+50 =100km/hour
initial distance between trains =200km
so time to impact=200/100 = 2hours
during this time the fly's velocity is 75km/hour
so in 2 hours the fly travels 2x75 = 150km