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 Two sets of Coins (Posted on 2005-10-07)
You have two sets of five coins. Each set has four real 30g coins and one 31g fake coin. It is easy to find the fake coins using a balance scale a total of four times, two weighings for each set.

Can you find a strategy which uses only three weighings?

 See The Solution Submitted by Brian Smith Rating: 3.5000 (2 votes)

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 3 simple steps | Comment 1 of 7
let one set be ABCDE ,the other abcde/
1st: ABC on the left abc -right
if one prevails , say left then the heavy coins are :one from the set A,B, C, plus either d or e.
two separate weighings: A vs B, and d vs e determine a heavy coin from each set.

if first weighing results in equality,try for
next AB vs de if equal C is not the heavy one,
so it is A or B and either d or e (third time will show the
heavy one- e.g. pick up A vs d )/
It is similar reasoning for one of either sides being heavier: leave it to you.

 Posted by Ady TZIDON on 2005-10-07 16:15:03

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