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 Replies: 467 / Views: 17,927 |
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Pillar of the Community
United States
539 Posts |
I already know my answer is wrong...never mind, how stupid of me
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Pillar of the Community
 United States
2605 Posts |
So far rickando has a way with the fewest weighings, but even he didn't get it!
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Pillar of the Community
United States
2605 Posts |
rikcando, your way works, but you still have too many weighings!
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Valued Member
Canada
287 Posts |
I know I am wrong, I am always wrong. It just is a matter of degree how far wrong I am.
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Pillar of the Community
United States
1031 Posts |
Weigh 40 coins on each side discarding the 40 coins from the heaviest side (1). Repeat with 20 coins on each side discarding the 20 coins from the heaviest side (2). Repeat with 10 (3), 5 (4), and 3 coins on each side (5). For the (6)th weigh in, weigh coin 1 and 2 discarding the heaviest or in case of a tie pick one. For the (7)th and final weigh in weigh the coin left on the scale and the 3rd and final coin. The counterfeit coin will be the one that weighs the least.
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Pillar of the Community
United States
1031 Posts |
I was trying to cook something and do this at the same time so it would be 2 coins on each side, not 3 for the 5th weighing. I finally turned off the stove so I didn't melt all my coins.
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Pillar of the Community
United States
2605 Posts |
Too many weighings, docs!
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Valued Member
Canada
287 Posts |
Ok, I have found a way to do it with 5 weighings
C'mon 11pm Friday
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Pillar of the Community
United States
2605 Posts |
Quote:
so it would be 2 coins on each side, not 3 for the 5th weighing. And then you'd do it with 6 times, as rikcando. |
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Valued Member
Canada
287 Posts |
oh no, rik learns quick. He now does it in 5 ! :)
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Pillar of the Community
United States
2605 Posts |
Could you do it in 4? 3? 2? 1?  |
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Pillar of the Community
United States
539 Posts |
I also can do it in 5 now. I should have just waited until all of the wrong answers were posted!! LOL
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Valued Member
Canada
287 Posts |
well bust my button, I can name the coin in 4 weighs !!
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Pillar of the Community
United States
4000 Posts |
It can be done in 4 weighings:
Divide the coins into 3 piles of 27 coins each.
1) Weigh pile A against pile B. If they are equal, then the counterfeit coin is in pile C, otherwise it is in the lighter pile of the first weighing.
2) Divide the suspect pile into 9 coins each and isolate the lighter pile again.
3) Divide that pile into 3 coins each and find the suspect pile once again.
4) Weigh one coinagainst another. Again if they are equal, the suspect coin is on the table. Otherwise, it is the lighter of the two that were weighed.
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Valued Member
Canada
287 Posts |
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Replies: 467 / Views: 17,927 |
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Posted 02/03/2011 11:15 pm
