Little Johnny is in the classroom, learning how to add. ""How much is two plus two, Johnny?"" asks the teacher. Johnny hesitates, looks at his hand, and starts counting with his fingers: ""One, two, three, four!"" he exclaims. ""No, no. Johnny,"" says the teacher. ""You can't use your hands. You have to count in your head. So, how much is four plus four, Johnny?"" she asks again. Johnny hides his hands behind his back and whispering to himself, counts, ""One, two, three, four... eight!"" he shou…