U2 has a concert that starts in 17 minutes and they must all cross a bridge to get there. All four men begin on the same side of the bridge. You must help them across to the other side. It is night. There is one flashlight. A maximum of two people can cross at one time. Any party who crosses, either 1 or 2 people, must have the flashlight with them.
The flashlight must be walked back and forth. It cannot be thrown and other tricks like that are not needed to solve the problem. The solution is simply a matter of allocating resources in a certain order. Each band member walks at a different speed. A pair must walk together at the rate of the slower man’s pace:
Bono: 1 minute to cross
Edge: 2 minutes to cross
Adam: 5 minutes to cross
Larry: 10 minutes to cross
For example: if Bono and Larry walk across first, 10 minutes have elapsed when they get to the other side of the bridge. If Larry then returns with the flashlight, a total of 20 minutes have passed and you have failed the mission.
This is one of my favorite brain teasers and I want to give you the satisfaction of figuring it out on your own. If you’re having a hard time, here’s a hint: There is a valid answer that doesn’t require tricks like throwing the flashlight or shining it backwards or having some other means of moving the flashlight.
There’s an assumption people often make that keeps them from solving this. Two members cross the bridge each time, but neither one of the two who crossed necessarily need to return. Think about how that would be possible. If you’re still stuck, use objects to simulate their movements. Use whatever you have laying around – pens, paper, erasers – and move them back and forth. Good luck!
6 Comments on "A U2 Concert"
Frodo Baggins says
March 9, 2014 @ 12:46
FOUND THE ANSWER!!!!!!!!!!!!!!!
June 1, 2014 @ 20:22
What is it?
Theresa Bagley says
June 26, 2014 @ 04:52
I got it!!
October 19, 2014 @ 08:33
Bono and Edge go first with flashlight (2 min
Edge goes back with flashlight (2 min)
Adam and Larry cross with flashlight (10 min)
Bono goes back with flashlight (1 min)
Bono and Edge cross with flashlight (2 min)
Riddle Mistress says
May 10, 2018 @ 16:34
Bono And Edge go with the flashlight, Edge goes back with the flashlight, then passes it to Adam and Larry to cross. Then, they pass it to Edge to go back, get Bono, and walk across the bridge
Impatient Person says
August 26, 2020 @ 19:58
Bono and Edge cross the bridge together. (2 minutes) Edge goes over (4 minutes) & give the flashlight to Larry and Adam. The they go over the bridge (14 minutes) & give the flashlight to Bono. Then Bono happily skips along (15 minutes) and then Bono and & Edge quickly rush over to the other side (17 minutes) of the bridge where the rest of their buddies are standing. Then getting in a taxi, (why didn’t they do that before?!) they go and play for all the very patient people waiting. Larry learns to walk faster, Adam writes a book, and the U2 band lives happily ever after.
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