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Based on Xkcd's Boat Puzzle

At the riverbank, a succession of people have given you a large lump of objects to transport across the river. These are:

  • 101 cabbages
  • 2 goats, one of which eats wolves
  • 4 wolves, one of which can operate the boat alone
  • 1 swarm of cabbage moths (counts as single object)
  • 1 colony of termites

There are some issues you'll have to deal with in transport, however. If you leave them alone, then the goats and moths will eat the cabbages, the wolves will eat the goats, and the termites will eat the boat.

Further complicating the matter is the runaway trolley heading towards you at breakneck speed, and your small boat that can only carry 4 things, including yourself (the swarm and colony each count as only 1 thing, while the cabbages count as 101 separate things).

What is the fewest number of crossings required to get across the river intact?

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  • $\begingroup$ Is this a puzzle or a joke? ... anyway it's a good one. $\endgroup$
    – WhatsUp
    Dec 4, 2021 at 15:38
  • $\begingroup$ @WhatsUp It's a puzzle $\endgroup$
    – Ichthys King
    Dec 4, 2021 at 15:39
  • $\begingroup$ The details imply any of the 4 wolves will eat any of the goats (but only one wolf can row), but only 1 of the 2 goats eats wolves. Can you edit that statement to be clearer? And for nomenclature purposes, how best to represent those? G/g for the eating/non-eating goats respectively? $\endgroup$
    – smci
    Dec 5, 2021 at 8:02
  • $\begingroup$ Also, it's not enough that one wolf can row the boat alone (e.g. with random contents or empty), it needs to be able to be given instructions of what to transport. And cooperate. And the time taken to explain the plan to the wolf doesn't count, and it never makes mistakes. Doesn't sound very predator to me. $\endgroup$
    – smci
    Dec 5, 2021 at 8:08
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    $\begingroup$ @smci Maybe he is a Wallstreet wolf, and just has got a good deal on any goats he can ...borrow. $\endgroup$
    – Bjorn Eriksson
    Dec 5, 2021 at 11:09

2 Answers 2

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It is not that difficult, actually. The number of crossings required is ...

73.

And here is how to do it.

schedule of boat crossings
The first thing is to isolate the goats and the moths from the wolves and the cabbages.
This solves all potential conflicts on the left side.

Then you go fetch the termites and the sailor wolf.

From now on you must stay on the right side to look after all these animals.
Send the sailor wolf collect the other wolves.

The trolley can dump into the stack of cabbages.

Finally, the sailor wolf retrieves the cabbages.

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    $\begingroup$ +1 for having "ma[d]e a spreadsheet". $\endgroup$
    – msh210
    Dec 4, 2021 at 20:53
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    $\begingroup$ "sailor wolf" sounds like an anime $\endgroup$
    – smci
    Dec 5, 2021 at 8:12
  • $\begingroup$ I fixed the misplaced "1". And the "sailor wolf" was supposed to be "sailing wolf" as Munroe used in the xkcd strip. But it sounds good like that. $\endgroup$
    – Florian F
    Dec 5, 2021 at 17:11
  • $\begingroup$ I imagine the sailor wolf wearing a tiny sailor cap $\endgroup$
    – QBrute
    Dec 6, 2021 at 11:02
  • $\begingroup$ Google "sailor wolf" as images and you will find it. $\endgroup$
    – Florian F
    Dec 6, 2021 at 15:22
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I have a completely different answer. I'm not sure if I'm reading too much into the wording or if this is the real intention of the question.

1 trip with only yourself on the boat.

Because

What is the fewest number of crossings required to get across the river intact?

It's a trick question. The final line only requires yourself to cross "intact". The objects don't matter.

Additionally the title

An overcomplicated Boat Puzzle

It's overcomplicated because there are many details that don't matter which makes it more complicated than it needs to be.

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  • $\begingroup$ Whether this answer works depends upon what must remain "intact", since if you go yourself several of the things you leave behind will no longer be so. $\endgroup$
    – bobble
    Dec 5, 2021 at 5:45
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    $\begingroup$ @bobble correct. This answer is entirely dependent on the wording of the last line. The subject of the sentence is yourself and it makes no mention of anything else so "intact" must be referring to you. I expect the question will be edited to disprove me. $\endgroup$
    – SkySpiral7
    Dec 5, 2021 at 5:48
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    $\begingroup$ The tags should clarify whether this is intended solution. There is optimization but no lateral-thinking. $\endgroup$
    – WhatsUp
    Dec 5, 2021 at 8:15
  • $\begingroup$ I am not sure this was intended solution, but the wording certainly weighs in that direction. $\endgroup$
    – Florian F
    Dec 5, 2021 at 17:24
  • $\begingroup$ @WhatsUp when I read the question this answer was my first thought (a serious answer). After posting it I quickly decided that this probably isn't the intension (after seeing the lack of lateral-thinking tag). Although I don't know if it makes sense for trick questions to be labeled as such. $\endgroup$
    – SkySpiral7
    Dec 13, 2021 at 0:51

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