# Crossing the bridge - Hard riddle

Thequ1ck
Posers and Puzzles 19 Nov '05 21:24
1. Thequ1ck
Fast above
19 Nov '05 21:24
4 musicians are on one side of a bridge at night and need to
reach the other side in the next 16 minutes.

They only have 1 flashlight and so must travel in pairs accross
the bridge, with one person returning with the flashlight for the next pair.
Going across, the pairs must walk at the speed of the slowest person.

The 4 musicians take 1,2,5 & 9 minutes to cross the bridge
respectively.

How do they manage to do it?

This is not a trick question but one of resource management.

2. BigDoggProblem
Court Jester
19 Nov '05 22:51
Originally posted by Thequ1ck
4 musicians are on one side of a bridge at night and need to
reach the other side in the next 16 minutes.

They only have 1 flashlight and so must travel in pairs accross
the bridge, with one person returning with the flashlight for the next pair.
Going across, the pairs must walk at the speed of the slowest person.

The 4 musicians take 1,2,5 & 9 mi ...[text shortened]... it?

This is not a trick question but one of resource management.

Solution I:
- 2 and 1 go over (2 min)
- 1 comes back (1 min)
- 9 and 5 go over (9 min)
- 2 comes back (2 min)
- 2 and 1 go over (2 min)
Total time = 16 minutes

Solution II:
- 2 and 1 go over (2 min)
- 2 comes back (2 min)
- 9 and 5 go over (9 min)
- 1 comes back (1 min)
- 2 and 1 go over (2 min)
Total time = 16 minutes

The main idea is to never waste time sending 9 or 5 back, and also to 'eliminate' the 5-minute guy from the addition.
3. Thequ1ck
Fast above
19 Nov '05 22:57
Originally posted by BigDoggProblem
Solution I:
- 2 and 1 go over (2 min)
- 1 comes back (1 min)
- 9 and 5 go over (9 min)
- 2 comes back (2 min)
- 2 and 1 go over (2 min)
Total time = 16 minutes

Solution II:
- 2 and 1 go over (2 min)
- 2 comes back (2 min)
- 9 and 5 go over (9 min)
- 1 comes back (1 min)
- 2 and 1 go over (2 min)
Total time = 16 minutes

The main idea ...[text shortened]... er waste time sending 9 or 5 back, and also to 'eliminate' the 5-minute guy from the addition.
Very good. Most people take many hours to solve that one.
The catch is understanding that the torch can be passed.
4. TheMaster37
Kupikupopo!
27 Nov '05 09:43
Heh, I know this riddle with a family. Daughter and son are the quickest, mother takes a bit longer and grandma takes the longest :p
5. 27 Nov '05 18:05
Originally posted by Thequ1ck
4 musicians are on one side of a bridge at night and need to
reach the other side in the next 16 minutes.

They only have 1 flashlight and so must travel in pairs accross
the bridge, with one person returning with the flashlight for the next pair.
Going across, the pairs must walk at the speed of the slowest person.

The 4 musicians take 1,2,5 & 9 mi ...[text shortened]... it?

This is not a trick question but one of resource management.

Heres mine,

2 & 1 = 2
2 = 2
5 & 9 = 9
1 = 1
2 & 1 = 2

Total = 16

Took a little while to figure out how to get 5 & 9 across together.
6. BigDoggProblem
Court Jester
28 Nov '05 04:36
Originally posted by nickhawker
Eh, just admit you stole the answer from me. How could you ignore it when it's the 2nd post in the thread?
7. 28 Nov '05 16:471 edit
Originally posted by BigDoggProblem
Eh, just admit you stole the answer from me. How could you ignore it when it's the 2nd post in the thread?
Because i didn't scroll down and hence didn't see your post till afterwards. You see there is this thing called willpower, it's quite useful.
8. BigDoggProblem
Court Jester
28 Nov '05 18:02
Originally posted by nickhawker
Because i didn't scroll down and hence didn't see your post till afterwards. You see there is this thing called willpower, it's quite useful.
You must have a tiny monitor if you have to scroll down just to see the 2nd post in a thread...
9. 28 Nov '05 20:28
Originally posted by BigDoggProblem
You must have a tiny monitor if you have to scroll down just to see the 2nd post in a thread...