Coins problem

  • Thread starter didi
  • Start date
3
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Hi,
I have the following to solve and I tried so many things but it is confusing. Here is the problem
Given 12 coins such that exactly one of them is fake (we don't know if it is heavier or lighter than the rest), and a pan scale, devise a procedure to identify the fake coin and whether it is heavier or lighter by doing no more than 3 weightings.

Thank you :smile:
didi
 

matt grime

Science Advisor
Homework Helper
9,394
3
A very famous problem that is alleged to have caused many problems with people at some important mathematical institution during WW2 (bletchley?) as they spent too much time trying to solve it. I'm sure that if you really don't want to spend time proving it the answer is googlable. But you really ought to try it and at least post your musings here. Though undoubtedly some one will sadly post the solution for you.
 
Try solving it with 3 coins in 2 tries first
 

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