Multiple choice general knowledge math & puzzles

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?

  1. 150 KM

  2. 175 KM

  3. 125 KM

  4. 137 KM
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A Correct answer
Explanation

The trains approach each other at 100 km/h (50 + 50), so they collide in exactly 2 hours (200 km ÷ 100 km/h). The fly continuously travels at 75 km/h during these 2 hours, covering 150 km total. This classic puzzle has an elegant solution - instead of calculating each leg of the fly's journey, simply multiply the fly's speed by the time until collision. This avoids summing an infinite geometric series.

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