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Topic: coins problem
Replies: 7   Last Post: Jun 16, 2009 10:34 PM

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Sarah Seastone

Posts: 1,240
Registered: 12/3/04
Re: coins problem
Posted: Jan 27, 1999 4:46 PM
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See if this helps:

12 coins problem - Frans Faase

At 3:02 PM -0500 1/27/99, Helena Verrill wrote:
>a little while ago, someone asked the following:
>if you have 12 coins, one of which is either
>heavier or lighter than the others, the others all
>being the same weight, how can you determine which
>one it it, and whether it's heavier or lighter, in
>three weighings.
>Well, I did't think about this problem until last
>weekend when I heard it for a second time.
>Anyway, it's not too hard to solve, but how about
>what is the minumum number of weighings that you
>need to determine which is the odd one, and whether
>it's heavy or light, from n coins?
>Eg, you can do 3 coins in 2 weighings,
>12 coins in 3, 38 coins in 4 weighings -
>I'd rather ask for what is the sequence a_n
>so that a_n is the maximum number of coins such
>that the odd one can be found (and said to be heavier
>or lighter). I'd guess this starts 3,12,38...
>but I can't find this sequence in Sloanes integer
>sequences, so presumably that means 38 is not the
>max you can do in 4 weighings... Anyone else tried?

Sarah Seastone
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