A wise teacher showed his three students that he had two red hats and three blue hats.

The three students would close their eyes, and while their eyes
were closed, the teacher would put a hat on each of their heads
(and hide the other two hats).

Then, one at a time, the students would open their eyes, look at
the other two students' heads, and try to guess which color hat
was on their own head.

Arturo, who was to go first, opened his eyes, looked at the
others' heads, and said he didn't know. Next, Belicia opened her eyes and looked at the others'
heads. Then she said she didn't know either. She couldn't tell for sure.

Carletta was third. She just stood there with her eyes still
closed tightly and a big grin on her face. "I know what color hat
I have on," she said.

And she gave the right answer.

Your problem is to figure out what color hat Carletta had on and
how she knew for sure. Remember: Carletta didn't even look!