Jump to content


Welcome to BrainDen.com - Brain Teasers Forum

Welcome to BrainDen.com - Brain Teasers Forum. Like most online communities you must register to post in our community, but don't worry this is a simple free process. To be a part of BrainDen Forums you may create a new account or sign in if you already have an account.
As a member you could start new topics, reply to others, subscribe to topics/forums to get automatic updates, get your own profile and make new friends.

Of course, you can also enjoy our collection of amazing optical illusions and cool math games.

If you like our site, you may support us by simply clicking Google "+1" or Facebook "Like" buttons at the top.
If you have a website, we would appreciate a little link to BrainDen.

Thanks and enjoy the Den :-)
Guest Message by DevFuse
 

Photo
- - - - -

Fly


  • This topic is locked This topic is locked
25 replies to this topic

#1 rookie1ja

rookie1ja

    Senior Member

  • Site Admin
  • PipPipPipPip
  • 1337 posts
  • Gender:Male
  • Location:Slovakia

Posted 30 March 2007 - 03:57 PM

A Fly - Back to the Cool Math Games
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.)

This old topic is locked since it was answered many times. You can check solution in the Spoiler below.
Pls visit New Puzzles section to see always fresh brain teasers.


Spoiler for Solution


Spoiler for old wording

  • 0

rookie1ja (site admin)
Optical Illusions
Support BrainDen

"To start: Press any key... Where's the 'any' key?" - Homer Simpson


#2 larryhl

larryhl

    Junior Member

  • Members
  • PipPip
  • 68 posts

Posted 05 June 2007 - 07:11 PM

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.
  • 0

#3 lukegaru

lukegaru

    Newbie

  • Members
  • Pip
  • 10 posts

Posted 03 July 2007 - 08:21 PM

150klm
  • 0

#4 Slick_Rick9009

Slick_Rick9009

    Junior Member

  • Members
  • PipPip
  • 20 posts

Posted 26 July 2007 - 09:39 AM

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.
  • 0

#5 captainobvious00

captainobvious00

    Newbie

  • Members
  • Pip
  • 2 posts

Posted 07 August 2007 - 08:10 AM

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
  • 0

#6 twilly

twilly

    Newbie

  • Members
  • Pip
  • 4 posts

Posted 14 August 2007 - 04:31 AM

i have one question, how can a fly go faster than a train?
  • 0

#7 mdsl

mdsl

    Junior Member

  • Members
  • PipPip
  • 51 posts

Posted 14 August 2007 - 08:43 PM

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.
  • 0

#8 tydis

tydis

    Newbie

  • Members
  • Pip
  • 3 posts

Posted 18 August 2007 - 11:44 PM

ok this might be a stupid question but how do you know it takes 2 hours? the puzzle never says so.
  • 0

#9 mdsl

mdsl

    Junior Member

  • Members
  • PipPip
  • 51 posts

Posted 20 August 2007 - 12:35 PM

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



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.
  • 0

#10 Dreaken667

Dreaken667

    Newbie

  • Members
  • Pip
  • 3 posts

Posted 24 August 2007 - 01:59 AM

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.
  • 0




0 user(s) are reading this topic

0 members, 0 guests, 0 anonymous users