If I remember the story correctly, when Gauss was in grade school, his teacher made his students do long practice problems before they would be allowed to go to play. One day the teacher had them add up all the numbers from one to one hundred, Gauss made the observation discribed above, and handed in the answer almost immediately. The teacher, thinking that Gauss was trying to cheat, scolded Gauss and told him to do the problem "the right way", when the answer Gauss found quickly turned out to be correct, the teacher was, to say the least, stunned.