The mathematician’s child and the economist’s child were in the third grade together, and the teacher asked,

«If one man with one shovel can dig a ditch in ten days, how long would it take ten men with ten shovels to dig the same ditch?»

 Both children raised their hands. The teacher said to the mathematician’s child, «Johnny, how long?» and Little Johnny said,

«One day, teacher.»

The teacher looked at the economist’s child and said, «John Maynard, is that right?»
Little John Maynard replied,

«Teacher, it all depends.»