You have five coins, apparently alike, but actually of different weights. You also have a two arm scale.
Can you manage to sort the coins in ascending order, using the scale only seven times?
Bonus question: can it be done in fewer weighings?
The bonus part is easier than the primary question: barring equality of weights (which is valid as they're all "different weights") there are 5! = 120 possible orders for the weights of the coins. Six weighings allows only 2^6 = 64 possible sequences of results of the weighingsnot enough to differentiate all the possible orders of weights.
Seven weighings is indeed informationtheoretically enough to distinguish 128 possibilities, but actually to set out a methodology in the present case is a different story. It might not be possible.

Posted by Charlie
on 20040531 10:16:07 