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# Fly

25 replies to this topic

### #21 rookie1ja

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Posted 04 April 2008 - 10:50 AM

I think this is a solid puzzle, if you want to make it a little more technically correct, it should say that the fly is flying at 75kph relative to ground. I only say this because as soon as i saw the words "the fly takes off from the train" I thought he was flying at 50kph from being on the train and you add that to the 75 (if it was relative to the train) for a total velocity of 125kph relative to ground. Its really probably not an issue for anyone other than me and most people would assume it, but it is more technical.

puzzle edited ... if that helps
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### #22 pgreen1911

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Posted 10 June 2008 - 09:11 PM

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

distance apart 200km/ 2 trains at 50km/hr
200/2*50
2
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### #23 beeblebrox

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Posted 24 September 2008 - 08:12 PM

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.

If this were in a vacuum you'd be right, but the air between the trains is actually moving at 0mph (presumably) so it still doesnt make sense that a fly can go 75 km/h. But this is a puzzle, and a very clever one at that, so I will stop with the annoying harshness of reality.
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### #24 Martini

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Posted 26 September 2008 - 08:07 PM

If this were in a vacuum you'd be right

mdsl's statement about a fly in a train is correct (although the riddle is not about a fly in a train). If the fly were in a vacuum, it couldn't fly at all.

but the air between the trains is actually moving at 0mph (presumably) so it still doesnt make sense that a fly can go 75 km/h.

Sure it does.
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### #25 rsaylors

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Posted 14 October 2008 - 08:12 AM

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

I have a problem here. By definition if they are moving at 50km/h towards each other then they are each moving an average of 25kph. I don't know why everyone seems to think that "50 km/h towards each other" means each train is moving at 50 kph towards the other train. If each train where moving an average of 50km/h then they would be moving at a rate of 100kmph towards each other.

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### #26 Scraff

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Posted 14 October 2008 - 06:07 PM

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

I have a problem here. By definition if they are moving at 50km/h towards each other then they are each moving an average of 25kph.

They are moving at the speed of 50 km/hour. That is describing the speed of each train. When we define the speed of a train, most of us do so with respect to the ground, not other moving objects.

"Two trains are moving at the speed of 50 km/hour next to each other."

We would say that each train is traveling at 50 km/hour because that's how fast they're traveling in respect to the ground. We wouldn't say they are traveling 0 km/hour.

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

Each train is traveling at 50 km/hour in respect to the ground.
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