Solve this:

There is a really wealthy kingdom and the princes mother wants to chose the smartest princess to marry her prince. So she invites every one from the whole country to come and gives them all an intelligence test. 3 of them get a perfect score. So she invites them to a room with 3 chairs and gives them the following instructions:

I will blindfold all of you and sit you on a chair. Then I will either put a red hat onto your head or none and will proceed to remove the blind folds.

If you see one red head raise your arm. If you see 2 red hats raise your arm. The first person who can tell me if she is wearing a red hat or not can marry my son.

The queen blind folds all of them and sits them on the chair. She then proceeds to put a red hat on each one (assume that it is impossible for the princesses to feel if a red hat was put on them or not) and removes the blind folds.

Immidiatly everyone raises their hands, but noone speaks and they just look at each other. Some time goes by and then one of them stands up and says: "I am wearing a red hat"

Explain how she knows this.

Lets see who can get it first