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Cross the 3 Couples


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9 replies to this topic

#1 umairnk

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Posted 24 August 2007 - 08:30 AM

Let A, B & C be the respective husbands of X, Y & Z.

Rules:
1. You need to take all 6 to the other side of the river along with the boat.
2. Atmost two can be on the boat at a time.
3. A wife cannot remain in the presence of a man(excluding her husband) at any side, except in that her own husband is with her i.e. AXB is possible, but XB is not.
4. All know boating.


Reply in steps. Use the same variables.
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#2 tanric

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Posted 24 August 2007 - 01:14 PM

Bit of trial and error at first, but pretty sure I got there.
Answer.JPG
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#3 bonanova

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Posted 24 August 2007 - 01:58 PM

1. You need to take all 6 to the other side ...


Please clarify - As you take them across the river, there can be no more than one of them with you in the boat?
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The greatest challenge to any thinker is stating the problem in a way that will allow a solution.
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#4 bonanova

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Posted 24 August 2007 - 02:49 PM

You can't do it taking one at a time, and taking them two at a time is trivial. So I'll answer the problem of how they do it themselves. [edit - one of my letters was wrong]

xy cross, x returns --- .. .y .. || Ax B. Cz
Ax cross, A returns -- .x .y .. || A. B. Cz
Cz cross, C returns -- .x .y .z || A. B. C.
AB cross, z returns - Ax By .. || .. .. Cz
Cz cross ------------- Ax By Cz || .. .. ..

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The greatest challenge to any thinker is stating the problem in a way that will allow a solution.
- Bertrand Russell

#5 tanric

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Posted 24 August 2007 - 03:32 PM

That will work bonanova, except that at some points a wife is in presence of a man that isn't her husband.

Eg. at step 2, "Ax cross, A returns -- .x .y .. || A. B. Cz", y is in the presence of A on the same side as x is getting out of the boat.
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#6 bonanova

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Posted 24 August 2007 - 03:50 PM

That will work bonanova, except that at some points a wife is in presence of a man that isn't her husband.

Your solution avoids that situation.
I think you solved a more difficult problem than was proposed.

I opted for my approach because
[1] It takes one fewer crossing
[2] I believe the conditions provide for a momentary situation where a woman is without her husband but with another man, so long as she does not remain that way when the boat leaves them.

Maybe the author can resolve whether my interpretation is permitted.
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The greatest challenge to any thinker is stating the problem in a way that will allow a solution.
- Bertrand Russell

#7 umairnk

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Posted 27 August 2007 - 07:52 AM

@ tanric
Well done! This is the only right solution as far as I know.

@ bonanova
Your interpretation is wrong. Your second step i.e. (Ax cross, A returns -- .x .y .. || A. B. Cz) is wrong because if A crosses and finds another woman, he won't want to return, would he??? .
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#8 impact504

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Posted 29 August 2007 - 03:45 PM

i hope these couples are on their way to counseling.
damn wheres the trust??
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#9 bonanova

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Posted 30 August 2007 - 01:55 PM

i hope these couples are on their way to counseling.
damn wheres the trust??


You mean we have to take a counselor across, too?
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The greatest challenge to any thinker is stating the problem in a way that will allow a solution.
- Bertrand Russell

#10 unreality

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Posted 30 August 2007 - 06:48 PM

And everyone knows counselors can only be in the boat with X or Y or C, and they can NOT row the boat. DUH!
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