There are 3 students Anirban, Bala and Chandu sitting in a circle. Their teacher has 5 *bindis* with her, 3 white ones and 2 black. She asks all of them to close their eyes and then she sticks one white *bindi *each to each one of their foreheads. Now they are asked to open their eyes.

They are sitting such that all of them face each other. Each one can watch the *bindis *on the other two's foreheads but not on their own. Neither are they allowed to know of the color of the *bindis *the teacher is left out with.

To prove their intelligence, they have to tell the teacher the color of the *bindi *on their own forehead.

If you suppose, lets say after a while one of them (let's say Bala) proves herself clever by being able to answer rightly the color of her *bindi*, i.e. white. The question is how could she logically arrive to that conclusion?

Also try to figure out how will the students find out the colour of their *bindis *if the *bindis *are not all white?