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+9 votes
2,442 views
asked Jun 18, 2013 in Challenge / Quizzes by Cupcake549 (32,490 points)

 

A volcano erupts in the dark of the night. Four people, carrying only one flashlight, run for their lives. They come to a canyon. There's a footbridge that spans the canyon. The bridge can only support 2 people at a time. Since it's dark, they must use a flashlight to cross. Therefore, after 2 people cross safely, one has to go back to bring the flashlight back to the other side.
 
The people, suffering from different injuries, travel across the bridge at different speeds. Person #1 takes 1 minute, person #2 takes 2 minutes, person #3 takes 5 minutes, and person #4 takes 10 minutes. Two people crossing the bridge will travel at the speed of the slower person. There are only 17 minutes before the lava destroys the bridge. Find a logical solution where all four people reach the other side safely in 17 minutes or less—but this solution cannot include having any of them go only halfway across, or go across in the dark, or throw the flashlight across, etc. AND REMEMBER: You also have to count the time it takes to go back across the bridge with the flashlight!


2 Answers

0 votes
answered Jun 18, 2013 by smile828 (32,100 points)
selected Jul 1, 2013 by Cupcake549
 
Best answer
This is a hard problem to solve for me.I don't know the answer. Is it even possible for the people to make it,because if you add up the numbers it is higher than the number 17.The total is 18 minutes.But, still they have to back to give the flashlight to the next person, so it would be more than 18 min..

Do you know the answer?
commented Jun 19, 2013 by Cupcake549 (32,490 points)
Yes
Soulution 1
1 person 1&2 cross the bridge-elapsed time 2 minutes
2 person1 returns-elapsed time 2 minutes
3 person 3&4 cross- elapsed time 13 minutes
4 person 2 returns- elapsed time 15 minutes
5 person 1&2 return- elapsed time 17 minutes

Solution 2 has person 2 returning in 2 and 1 returning in 4
commented Jun 19, 2013 by smile828 (32,100 points)
Thanks for the answer. I would never have guessed that.
commented Jun 19, 2013 by Cupcake549 (32,490 points)
You are welcome! I love brain teasers so I found some and wanted to see If you could get them!
+1 vote
answered Jul 24, 2013 by kristy84 (2,820 points)
edited Apr 2, 2017

Where in the world did you get this question ? If you made it up without any help your grr8 at puzzles ! 2 b honest with you I don't know the answer .surprise

commented Jul 24, 2013 by Cupcake549 (32,490 points)
no i did not make this up but it was on a website i have to find it though, so i will post it on here when i do!

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