Coin Problem

You are given 9 gold coins that look identical. One is
counterfeit and weighs a bit greater than the others, but
the difference is very small that only a balance scale can
tell it from the real one. You have a balance scale that
costs 25 USD per weighing.

Give an algorithm that finds the counterfeit coin with as
little weighting as possible. Of primary importance is that
your algorithm is correct; of secondary importance is that
your algorithm truly uses the minimum number of weightings
possible.

HINT: THE BEST ALGORITHM USES ONLY 2 WEIGHINGS!!!

Answer Posted / pawan jain

1. Divide the coins in 3 groups of 3 coins each
2. Put 2 groups in the weighing scale
3a. If both the groups weigh equal
1. Pick 2 coins from the 3rd group and put in weighing scale
2. If they weigh equal, the 3rd coin is counterfeit.
Else the coin which weigh more is counterfeit
3b. If they do not weigh equal, pick the group with more
weight and do steps 3a1 and 3a2.

Is This Answer Correct ?    40 Yes 13 No



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