Young Miss Cadence is teaching calculus and asks Johnny: 'Johnny, 3 crows are sitting on the roof of the barn. You get your gun and shoot one down. How many crows are left on the roof?' After a long contemplation Johnny answers: ""None, Miss Cadence."" Miss Cadence looks surprised and asks him to try again. ""I'm sure it's none. You shoot one down and the other crows fly again"" Young Miss Cadence giggles and comments : ""No, Johnny.. It's two. But I like the way you think"" ""I've got a questio…