⟩ A visiting school superintendent noticed that whenever he asked one class a question all the children would put up their hands. Moreover, although the teacher always chose a different child to answer, the answer was always correct. Why?
The teacher instructed her pupils always to raise their hands when a question was asked whether they knew the answer or not. If they did not know the answer they should raise their left hand. If they were sure they know the answer they should raise their right hand. The teacher chose a different child each time, but always one who had raised his or her right hand.
