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.
Bono (1) walks over with Edge (2), 2 minutes, Bono walks back, 1 minute (3 total), Larry (10) and Adam (5), walk across, 10 minutes (13 total), Edge Walks Back, 2 minutes (15 total), Edge and Bono walk back, 2 minutes (17 total)
To solve this puzzle and get all four members of U2 across the bridge within 17 minutes, you can follow these steps:
1. Bono and Edge cross the bridge together, taking 2 minutes. Bono, being the faster of the two, will be the one who returns with the flashlight.
2. Bono returns with the flashlight, taking 1 minute.
Total time elapsed: 2 minutes.
3. Larry and Adam cross the bridge together, taking 10 minutes. Since Larry, being the slower one, determines the pace, this step will take 10 minutes.
Total time elapsed: 12 minutes.
4. Edge returns with the flashlight, taking 2 minutes.
Total time elapsed: 14 minutes.
5. Bono and Edge cross the bridge together again, taking 2 minutes.
Total time elapsed: 16 minutes.
6. Finally, Bono returns with the flashlight, taking 1 minute.
Total time elapsed: 17 minutes.
All four members of U2 have successfully crossed the bridge within the given time frame.
To solve this puzzle, you need to carefully plan the crossing of the bridge by considering both the time taken and the order of crossing. Here's the step-by-step solution:
1. First, Bono and Edge cross the bridge together, taking 2 minutes. Bono being the faster of the pair ensures the minimum time is used.
Time elapsed: 2 minutes
2. Bono takes the flashlight and returns back to the starting side in 1 minute.
Time elapsed: 3 minutes
3. Adam and Larry then cross the bridge together, taking 10 minutes. Since Larry is the slower one, this is the best pairing to minimize overall time.
Time elapsed: 13 minutes
4. Edge takes the flashlight and goes back to the starting side in 2 minutes.
Time elapsed: 15 minutes
5. Finally, Bono and Edge cross the bridge together for the last time, taking 2 minutes.
Time elapsed: 17 minutes
At this point, all four band members have successfully crossed the bridge, and exactly 17 minutes have passed.
It's important to note that in this solution, the fastest band members (Bono and Edge) are utilized to their maximum potential by always taking the flashlight on the return trips, ensuring the overall time is minimized.