[rookie1ja]

A Fly - Back to the Logic 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?
(There is a complicated and an easy way to solve this math brain teaser.)

Spoiler for Solution:

Fly - solution
There is a complicated way counting a sequence. Or simply knowing that if the fly is flying the 2 hours still at the same speed of 75 km/h then it flies a distance of 150 km.

Spoiler for old wording:

Two trains 200 km from each other are moving at the speed of 50 km/hour towards each other. From one train a fly takes off (Edit: at the moment the trains are 200 km from each other), flying straight (upon the rails) to the other train at the speed of 75 km/hour (Edit: 75km/hour relative to ground), bounces away from it and flies back to the first train. This is repeated till the trains crash into each other and the fly is smashed.
What distance is the fly able to fly until its death?
(There is a complicated and an easy way to solve this math brain teaser.)

[larryhl]

good type of question to know for interviews =)

the sequence takes too long. just realize the fly will only be able to fly for 2 hours and multiply by speed to get distance.

[lukegaru]

150klm

[Slick_Rick9009]

I just want to say that I am very proud of this specific question because it is the only one I've seen that doesn't have the same questions and the same wrong answers being repeated a hundred times. Wrong answers are fine. But if you read and find out that they were already proven wrong, then you wouldn't be posting it. And if you're going to post something, shouldn't you read the previous posts to make sure you're not repeating? That happens a lot and this is the first I've seen that it hasn't happened. I'ts made a nerd very happy.

[captainobvious00]

what u have to take into consideration is that when the fly hits the other train, it will die. it would have to slow down first. then when it goes back, it will have to speed back up, therefore causing less travel time/distance

[twilly]

i have one question, how can a fly go faster than a train?

[mdsl]

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i have one question, how can a fly go faster than a train?

Easy, if the fly is inside the train and flys in a relative direction equal to the direction of the train, the fly will be going faster than the train relative to the tracks.

As it applies in this question, i don't know. It's just a puzzle.

[tydis]

ok this might be a stupid question but how do you know it takes 2 hours? the puzzle never says so.

[mdsl]

Quote

ok this might be a stupid question but how do you know it takes 2 hours? the puzzle never says so.

Quote

Two trains 200 km from each other are moving at the speed of 50 km/hour towards each other.

Each train is going 50 km/hour, they are traveling in opposite directions towards each other, and they are initially 200 km apart. The distance between the trains is decreasing at a rate equal to the sum of the speed of each train, or 100 km/hour.

It will take 2 hours to close the gap.

[Dreaken667]

I'd like to point out that there is a minor detail which has not been considered. Assuming that the fly begins his suicidal flight at the precise time that the trains are at their original points, then the calculation presented would be correct. However, the puzzle, as stated, does not in fact say when the fly begins his spiraling death. If he were to start flying half way through the trip for example, then he would only travel 75km. Therefore, unless the puzzle is reworded, the answer would rely on the point in which the fly has his nervous break down and decides that existence is futile.