"Math Knowledge" joke

Two mathematicians were having dinner in a restaurant, arguing about the
average mathematical knowledge of the American public. One mathematician
claimed that this average was woefully inadequate, the other maintained
that it was surprisingly high.
"I'll tell you what," said the cynic, "ask that waitress a simple math
question. If she gets it right, I'll pick up dinner. If not, you do."
He then excused himself to visit the men's room, and the other called
the waitress over.
"When my friend comes back," he told her, "I'm going to ask you a question,
and I want you to respond 'one third x cubed.' There's twenty bucks in
it for you." She agreed.
The cynic returned from the bathroom and called the waitress over. "The
food was wonderful, thank you," the mathematician started. "Incidentally,
do you know what the integral of x squared is?"
The waitress looked pensive; almost pained. She looked around the room, at
her feet, made gurgling noises, and finally said, "Um, one third x cubed?"
So the cynic paid the check. The waitress wheeled around, walked a few
paces away, looked back at the two men, and muttered under her breath,
"...plus a constant."