You have 12 coins. They are completely identical except six of them weigh 24g and the other six weigh 25g. You have only a balance scale to sort them out. What is the minimum number of weighings which guarantees all the coins to be sorted?
You can always do it simply in 10 weighings..
Take one coin and designate it the "master" coin.. Take each each of the other coins in turn and weigh them against this one. At some point you will find a coin that is heaver or lighter than the master. Also, you will find 5 other coins of the same weight as the master. Once you have done both of these, you are done. This could be as few as 6 weighings, or as many as 10. There is never any point in weighing the last coin, since you know what it must be....
But I think Charlie's worst case of 9 is best.
Edited on January 19, 2004, 3:30 pm
Simple approach
