[net.puzzle] coin weighing puzzle

israel@umcp-cs.UUCP (05/28/84)

You are given 12 coins and a balance.  Eleven of them are the same
weight.  The other coin is either heavier or lighter.  Your mission,
should you choose to accept it, is to discover which coin it is that
has the non-standard weight, and whether it is heavier or lighter than
the standard weight.  You can use the balance for comparing the weights
of two different groups of coins.  You must accomplish this with three
weighings or less.

rainbow@ihuxe.UUCP (05/30/84)

Question:How to find the counterfeit coin in a group of 12 given that it
         weighs differently. At your disposal is one balance usable 3 times.
         Also determine if it weighs more or less than the standard.
Answer:The key to the solution is to wiegh four opposite four the first time.
       This narrows the pile with the counterfeit coin down to four. Now just
       weigh the first two and the last two seperately to narrow it down to one