The Bridge Puzzle...

[DavidHooper]

There are 4 people, called A,B,C,D, who want to cross a bridge in the dark. They only have one torch between them. The bridge can only hold a maximum of two people at once. A can cross in 1 minute, B in 2 minutes, C in 5 and D in 10 minutes. The other rule is that if two people cross, they go at the pace of the slower person.

So for instance, A could cross over with B. This would take 2 minutes. Then B might return with the torch (which takes 2 minutes) to help C across. This crossing would take 5 minutes. Then B returns again (another 2 minutes) to help D across which takes 10 minutes. Total: 21 minutes.

How can they cross most quickly?

Btw, lets invent some notation to avoid confusion. AB|CD shows A and B are on the original side and C and D have crossed. So the above example reads:

ABCD|
CD|AB <2 mins>
BCD|A <2 mins>
D|ABC <5 mins>
BD|AC <2 mins>
|ABCD <10 mins>
(Total 21 mins)

[crptcblade]

ABCD|
CD|AB <2 mins>
ACD|B <1 min>
D|ABC <5 mins>
AD|BC <1 mins>
|ABCD <10 mins>
(Total 19 mins)

would this not be the fastest?

[beachbum]

Hi
17 mins is fastest i think

AB cross = 2 mins
A returns = 1 min (3)
CD cross = 10 mins (13)
B returns = 2 mins (15)
AB cross = 2 mins (17)
Regards
Stuart

[DavidHooper]

Top marks beachbum.

[Cheitan]

It's a bridge, not an obstacle course, they can cross it in the dark, darn fools!

Ah yes, I always have the wisest answer!

Doesn't answer the question, but alteast they get across

[DavidHooper]

lol

[Kaverin]

If this bridge can only hold 2 people at once, I don't know if I'd be too keen on crossing it, with or without a torch . That does remind me of a similar thing. It's called the Farmer's Dilemma I think (and if it isn't, that'll suffice).

A farmer must cross a river with his three items to get them to the market to sell them. He has a fox, a hen, and a basket of corn. Along the way he must cross a river. The fox and hen can't cross by themselves, so he must carry them across himself, but can only take one at a time. The problem is, if he takes the fox and leaves the hen alone with the corn, the hen will eat it. If he takes the corn and leaves the fox with the hen, the fox will eat the hen. What's the minimum number of total trips needed for the farmer to get his goods across the river without losing any? You can use this notation if you want:

Y = you (the farmer)
F = fox
H = hen
C = corn
| = river

start:
YFHC|

end:
|YFHC

[beachbum]

Hi all
Yeah that farmer one is pretty easy. Actually, there is a funny site here that lets u do these puzzles interactively. I tried a few months ago and cos i am such a super genius they were dead simple. Hope others enjoy them

http://www.plastelina.net/examples/games/index.html

Regards
Stuart

[Kaverin]

You could have answered though. I was hoping that someone would.

[beachbum]

Originally posted by Kaverin
You could have answered though. I was hoping that someone would.

LOL ok!!!! Geesh pushy

1. Farmer and chicken (mmm chicken)
2. Comes back self
3. Farmer and Fox (u sure a farmer would keep a fox?)
4. Brings chicken back
5. Farmer and corn
6. Comes back self
7. Farmer and chicken

Try the missionary one on that site i gave u ! is funny. Also, i see they have a new king and horse one (game 4).. ahhhh got it in one!! Answer is "Terrific"
Regards
Stuart

[paulw]

The answer is 5 minutes.

A crosses with B (ON HIS BACK hehe) 1m CD|AB
A returns 2m ACD|B
A crosses with C 3m D|ABC
A returns 4m AD|BC
A crosses with D 5m |ABCD - A is knackered.

Cheers,

P.

[DavidHooper]

lol. A is knackered.

[MartinSmith]

Actually, there is a funny site here that lets u do these puzzles interactively. I tried a few months ago and cos i am such a super genius they were dead simple

So BeachBum do you remember how to do game 4?

[MartinSmith]

Sorry, Scrub that I just found this thread http://forums.vb-world.net/showthrea...threadid=99448