Bridge Puzzle

 

Solution

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Solution by Jensen Lai

1. A and B go over... 2 mins.
2. A comes back... 3 mins.
3. C and D go over... 9 mins.
4. B comes back... 11 mins.
5. A and B go over... 13 mins.

Solution by Hüsnü Sincar

A=1 min B=2 min C=5 min D=6 min
Step Direction Couple Duration (min)
1 > AB 2
2 < A 1
3 > CD 6
4 < B 2
5 > AB 2

Solution by Nicole Takahashi

Here is a solution to the Bridge and Flashlight problem. Recall the labeling as

A = 1 minute
B = 2 minutes
C = 5 minutes
D = 6 minutes

1) A and B cross.
2 minutes pass, 2 minutes total

Side 1: C, D
Side 2: A, B

2) B crosses back (please see Note).
2 minutes pass, 4 minutes total

Side 1: B, C, D
Side 2: A

3) C and D cross.
6 minutes pass, 10 minutes total

Side 1: B
Side 2: A, C, D

4) A crosses back.
1 minutes passes, 11 minutes total

Side 1: A, B
Side 2: C, D

5) A and B cross.
2 minutes pass, 13 minutes total

Side 1: Nobody
Side 2: A, B, C, D

Note) In step (2) A could have crossed back leaving B behind. It may seem like that would save another minute. However, in step (4) where A would have crossed back, he's not there anymore. But B is, so now we would have the same total minutes again. Just a small variation of this soln.

Thank you :)

Solution by Tanya Bulls

To solve this puzzle first you have to have a left and right side of the bridge. All four people are on the right side of the bridge. 

The first to cross to the left side of the bridge are the 1 and 2 minute persons. This leaves 11 minutes. 

The 2 minute person stays on the left side while the 1 minute person goes to the right side with the flashlight, leaving 10 minutes. 

The 1 minute person stays on the right side while the 5 and 6 minute person goes to the left side, leaving 4 minutes. 

Now the 2, 5 and 6 minute person are on the left and the 1 minute person on the right. The 2 minute person goes back over the bridge with the flashlight, leaving 2 minutes. 

Now, the 5 and 6 minute persons are on the left and the 1 and 2 minute persons are on the right. Finally, the 1 and 2 minute persons cross to the left side of the bridge leaving 0 minutes left and all people on the left side.

Good Luck

Solution by Nigel Wilson

A goes with B : 2mins
A returns : 1min
C goes with D : 6 mins
B returns : 2min
A goes with B : 2min

Total : 13 mins

Solution by Terry & Lisa

a and b go over. a comes back. c and d come over. b comes back. a and b go over and you are finished.
1  2      1      5  6      2       1  2 
  2   +   1   +   6   +   2   +   2   =equals= 13!!!

Solution by Alex Packard

Here is the solution. The reader probably keeps getting 15 minutes.

A and B go across 2 min
A comes back 1 min
C and D go across 6 min
B comes back 2 min
A and B go across 2 min

2+1+6+2+2 = 13 
It is the same result whether A or B come back first, but they must come back second.

Posted: January 24, 2002  |  Last Updated: July 8, 2007
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