A math professor was explaining a particularly complicated calculus 
concept to his class when a frustrated pre-med student interrupts him. 
"Why do we have to learn this stuff?" the pre-med blurts out. The 
professor pauses, and answers matter-of-factly: "Because math saves 
lives." "How?" demanded the student. "How on Earth does calculus save 
lives?" "Because," replied the professor, "it keeps certain people out 
of medical school."