Thews40 Posted January 11, 2008 Share Posted January 11, 2008 There are four people who need to cross a bridge at night. The bridge is only wide enough for two people to cross at once. There is only one flashlight for the entire group. When two people cross, they must cross at the slower member's speed. All four people must cross the bridge in 17 minutes, since the bridge will collapse in exactly that amount of time. Here are the times each member takes to cross the bridge: Person A: 1 minute Person B: 2 minutes Person C: 5 minutes Person D: 10 minutes So, if Person A and C crossed the bridge initially, 5 minutes would elapse, because Person C takes 5 minutes to cross. Then, Person A would have to come back to the other side of the bridge, taking another minute, or six minutes total. Now, if Person A and D crossed the bridge next, it would take them 10 minutes, totaling to 16 minutes. If A came back, it would take yet another minute, totally 17... the bridge would collapse with A and B on the wrong side. How can all four people get across the bridge within 17 minutes? Quote Link to comment Share on other sites More sharing options...
The Wolf Posted January 11, 2008 Share Posted January 11, 2008 (edited) Put C and D on the shoulders of A and B...and you are finished in 2 minutes. Since only width dimensions are given, I am assuming that there are no height restrictions. Edited January 11, 2008 by The Wolf Quote Link to comment Share on other sites More sharing options...
tonorator Posted January 11, 2008 Share Posted January 11, 2008 There are four people who need to cross a bridge at night. The bridge is only wide enough for two people to cross at once. There is only one flashlight for the entire group. When two people cross, they must cross at the slower member's speed. All four people must cross the bridge in 17 minutes, since the bridge will collapse in exactly that amount of time. Here are the times each member takes to cross the bridge:Person A: 1 minute Person B: 2 minutes Person C: 5 minutes Person D: 10 minutes So, if Person A and C crossed the bridge initially, 5 minutes would elapse, because Person C takes 5 minutes to cross. Then, Person A would have to come back to the other side of the bridge, taking another minute, or six minutes total. Now, if Person A and D crossed the bridge next, it would take them 10 minutes, totaling to 16 minutes. If A came back, it would take yet another minute, totally 17... the bridge would collapse with A and B on the wrong side. How can all four people get across the bridge within 17 minutes? A and B go over together - 2 minutes elapsed A runs back and gives the flashlight to C - 3 minutes elapsed C and D cross together - 13 minutes elapsed B runs back with the flashlight - 15 minutes elapsed A and B go over together - 17 minutes elapsed Quote Link to comment Share on other sites More sharing options...
Big John Posted January 11, 2008 Share Posted January 11, 2008 The bridge is only wide enough for 2 across, but nothing says there can't be 2 rows of 2 each, with the back row right behind the first so all can see the light from the flashlight., so all 4 together can cross the bridge in 10 minutes. Quote Link to comment Share on other sites More sharing options...
SF409ers Posted January 11, 2008 Share Posted January 11, 2008 A and B go over together - 2 minutes elapsedA runs back and gives the flashlight to C - 3 minutes elapsed C and D cross together - 13 minutes elapsed B runs back with the flashlight - 15 minutes elapsed A and B go over together - 17 minutes elapsed Quote Link to comment Share on other sites More sharing options...
jelap1 Posted January 11, 2008 Share Posted January 11, 2008 A and B cross together and B returns (4 mins) D and C cross together and A returns (11 mins) A and B cross together (2 mins) Quote Link to comment Share on other sites More sharing options...
Savage Beatings Posted January 11, 2008 Share Posted January 11, 2008 Person A is obviously a crack head. He uses the flashlight to crush the skulls of Persons B, C and D... he then runs back and forth across the bridge 8 times before he jumps to his own death. Quote Link to comment Share on other sites More sharing options...
BeeR Posted January 11, 2008 Share Posted January 11, 2008 fluck it, let D's dumb pokey ass swim. Quote Link to comment Share on other sites More sharing options...
The Wolf Posted January 11, 2008 Share Posted January 11, 2008 Person A is obviously a crack head. He uses the flashlight to crush the skulls of Persons B, C and D... he then runs back and forth across the bridge 8 times before he jumps to his own death. Now THAT is some out of the box thinking! Person A --------- > Quote Link to comment Share on other sites More sharing options...
detlef Posted January 11, 2008 Share Posted January 11, 2008 Person A is obviously a crack head. He uses the flashlight to crush the skulls of Persons B, C and D... he then runs back and forth across the bridge 8 times before he jumps to his own death. Quote Link to comment Share on other sites More sharing options...
Caveman_Nick Posted January 11, 2008 Share Posted January 11, 2008 The bridge is only wide enough for 2 across, but nothing says there can't be 2 rows of 2 each, with the back row right behind the first so all can see the light from the flashlight., so all 4 together can cross the bridge in 10 minutes. I was just about to post the same thing. Quote Link to comment Share on other sites More sharing options...
Ursa Majoris Posted January 11, 2008 Share Posted January 11, 2008 Give the flashlight to the slow guy then all go one behind the other with a hand on the guy in front's shoulder. Ten minutes. Quote Link to comment Share on other sites More sharing options...
Fatman Posted January 11, 2008 Share Posted January 11, 2008 Helicopter. Quote Link to comment Share on other sites More sharing options...
cre8tiff Posted January 11, 2008 Share Posted January 11, 2008 The cannibals stew the missionaries as the fox slaughters the geese who are eating the grain. Quote Link to comment Share on other sites More sharing options...
Grits and Shins Posted January 11, 2008 Share Posted January 11, 2008 Why exactly is a flash light needed to cross the bridge in the first place? And is sky the old fart that can't get across the bridge in under 10 minutes? If it is sky he can't see anyway and the flash light would only be for show. Why couldn't they walk single file? Or as BJ suggests two sets of two? Quote Link to comment Share on other sites More sharing options...
Thews40 Posted January 12, 2008 Author Share Posted January 12, 2008 The bridge is only wide enough for 2 across, but nothing says there can't be 2 rows of 2 each, with the back row right behind the first so all can see the light from the flashlight., so all 4 together can cross the bridge in 10 minutes. good out-of-the-box input (C+)... I know you figured it out anyway which would have given you an A. I wish I could tell you where this question was actually posed... let's just assume you are in a pressure situation and had two minutes to answer this correctly ... would you crack under pressure? Quote Link to comment Share on other sites More sharing options...
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