There are 27 pieces of gold coin.
Among them, 26 pieces are genuine gold coins and one is fake gold coin lighter than the genuine coin.
How many times should I measure it to find a false gold coin at the number of times as less as possible by putting gold coins on the even balance ?
Among them, 26 pieces are genuine gold coins and one is fake gold coin lighter than the genuine coin.
How many times should I measure it to find a false gold coin at the number of times as less as possible by putting gold coins on the even balance ?
Answer
You can find the group which fake coin is included if the balance inclined to either side.
If not inclined, you can find The false one is in C group.
Therefore you can find the false by three times measurement.
Three times
Solution
First time: After being divided into groups A, B, and C each nine sheets of 27 pieces, you measure A and B of them by the even balance.
You can find the group which fake coin is included if the balance inclined to either side.
If not inclined, you can find The false one is in C group.
Second time: If you measure by the same way as the first and in portions of three sheets of nine, three pieces that contains the fake is found.
Third time: it is only necessary to be measured two of the three pieces.
Therefore you can find the false by three times measurement.
