"Excuse me, Professor, could you please help me with this calculus problem?"

"Okay, but only if it's something quick, I'm a very busy man," the mathematician replied.

"I'm having difficulty with this integral."

"Let me see," said von Neumann, who, after doing some mental calculations, replied,

"All right, young man, the value of that definite integral is 2/5π."

The student persisted,

"I know, Professor, the answer is on the back. I'm having trouble getting there. I can't figure out the solution strategy."

"Okay, let me see it again."

Neumann did his calculations again, still mentally, and concluded,

"The answer is 2/5π."

Visibly frustrated, the student said,

"Professor, I know the answer, but I don't know how to find it..."

"What do you want, my boy! I approached the problem in two different ways!".