Logic puzzle from http://okmij.org/ftp/kakuritu/StrangeLoop.pdf

Problem

"U2" has a concert that starts in 17 minutes and they must all
cross a bridge to get there. They stand on the same side of the
bridge. It is night. There is one flashlight. A maximum of two
people can cross at one time, and they must have the flashlight
with them. The flashlight must be walked back and forth. A
pair 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 rst, 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.

Solution

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Bono and Edge cross first and Bono comes back = 3 minutes
Adam and Larry cross and Edge comes back = 12 more minutes -> 15 minutes
Bono and Edge cross                      = 2 more minutes -> 17 minutes