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?
Take two coins and place them on the balance. One will weigh more than the other if this is the case then it will take 6. If there is a weighing and they are equal leave them to the side. This will be the seventh weighing by taking one of the coins that were equal and balancing it with one of the other coins that you know the weight of.