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Five People on Two Bridges (Posted on 2005-06-25) Difficulty: 2 of 5
In the puzzle Four people on a Bridge we met four people who needed to cross a bridge at night. In this puzzle, there are five people who must cross two sequential bridges at night. As in the original puzzle, there are some hindrances:

The bridges can only support two people crossing at a time.

Each person has a different speed in which they can cross: 10 minutes, 7 minutes, 5 minutes, 2 minutes, and 1 minute.

They have only two flashlights to share among them.

What is the shortest amount of time it will take for all five people to cross both bridges?

See The Solution Submitted by Erik O.    
Rating: 3.8000 (5 votes)

Comments: ( Back to comment list | You must be logged in to post comments.)
so much more | Comment 35 of 41 |
There is so much more to know;
a) like can one person stay alone in the dark?
b) Must each person have a light near them at all times?
c) Is there a limit as to how long the torches will last?
d) Can people stop in between bridges?
e) If 2 people are crossing do they travel at the speed of the   slower?

assuming a = yes b = no c = no d = yes e = yes
1 = 1 min 2 = 2 min 3 = 5 min 4 = 7 min 5 = 10 min

while 4 & 5 cross to end 1st bridge = 5 mins
when they start over 2 nd bridge 2 & 3 cross to middle as 4 & 5 just finished their 2nd 5 mins over 2nd brige. = 5 mins
Then when they done 2 & 3 start across 2nd bridge and 1 starts to cross 1st bridge = 2.5 mins
then 1 has to cross 2nd bridge = .5 mins

then fastest time to cross would be 13 mins

you can play with this taking the different assumptions I listed as different values count as true or false for getting to differnt solutions, keep the brain busy.

I know this isn't really a solution just sorta more to the problem, but I find it interesting when there is so obviously a chance to play with problems in your own way.

  Posted by Tammy Roy on 2005-07-12 16:53:18
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