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Tue 10 Jun, 2003 11:02 am
Heres the situation...
Imagine a river. There are four boats on the right side of the river and you want to take all of them to the left side. Each boat takes a certain amount of time to cross the river. One boat takes 8 minutes, one takes 4 minutes, one takes 2 minutes and the last one takes 1 minute. You are allowed to take one boat of a smaller time and put it inside a boat of a larger time and take it across. So for example you can put the 4 minute boat inside the 8 minute boat and take it across for a time of 8 minutes. However, you are now stuck on the left side and must then take one of the boats back to the right side to pick up the remaining two boats. So if you took the 4 minute boat back, you would have a total of 12 minutes and only the 8 minute boat on the left side. If this is confusing let me know, i'll try to clarify. The question is, how long will it take to get all four boats to the left side?
Most people find the answer to be 16 minutes. (Put the 1 minute boat inside the 8 minute boat and take it across and bring the 1 minute boat back, then put the 1 minute boat in the 4 minute boat bring it across, take the 1 minute boat back, put it in the 2 minute boat and take them across 8 min + 1 min + 4 min + 1 min + 2 min = 16 minutes) However this is incorrect, or so i'm told. The correct answer I believe was 15 minutes. Can anyone explain how to get this?
Bohemian,
Welcome to a2k. I've just enjoyed puzzling over this but I can't see how it can be less than 16 minutes, using the method you suggest.
I'm assuming (as you do) that there's no chance of "stacking" boats, so the obvious answer must use the 1 min boat as the means of getting back.
There's a minimum of 8+4+2 (each trip with the 1 min boat) plus 2 return crossings of 1 min each...I don't see how it could be less than 16.
I await some visionary with the answer...
KP
My parents went away on a weeks vacation??
Ok, here's a hint i guess the both of you been waiting for.
Ya gotta stop looking at that 1 min. boat as the most useful. The quickest way to git the slow boats across is to stack them together. You'll actually save time by putting the 4 boat in the 8 boat.
Maybe you want to take another stab at that 15 min. goal at this point. If you still give up, read on to the next post...
S,
Between fire and ice, sort of a lukewarm water...
Ok, since you've scrolled down this far,
- Start
8/4/2/1 river nothing
time: 0 min
- put the 1 boat in the 2 boat and cross..
8/4 river 2/1
time: 2
- take the 2 boat back..
8/4/2 river 1
time: 4
- ** put the 4 boat in the 8 boat and cross **
2 river 8/4/1
time: 12
- take the 1 boat back..
2/1 river 8/4
time: 13
- put the 1 boat in the 2 and cross as the light of victory shines upon you..
nothing river 8/4/2/1
time: 15!!
I Hope this helps and my diagrams aren't too confusing. I think there's some variation with a tunnel and a torch??
S,
The variation I know of is with a torch and a log bridge.
Nice job casino-hat!
I was thinking about a similar puzzle where you leave stuff halfway.
But you can't do that with a river, can you?
i know of a similar one where its ppl on a bridge though.
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