I'm

amazed that this one hasn't been posted yet:

Why is six afraid of seven?

Or this one:

What do you get when you divide the circumference of a jack-o-lantern by its diameter?

Oh I should stop this...

What is the first derivative of a cow?

"Divide fourteen sugar cubes into three cups of coffee so that each cup has an odd number of sugar cubes in it."

"That's easy: one, one, and twelve."

"But twelve isn't odd!"

"It's an odd number of cubes to put in a cup of coffee..."

"The number you have dialed is imaginary. Please, rotate your phone by 90 degrees and try again..."

A physicist, a statistician, and a (pure) mathematician go to the races and place bets on horses.

The physicist's horse comes in last. "I don't understand it. I have determined each horse's strength through a series of careful measurements."

The statistician's horse does a little bit better, but still fails miserably. "How is this possible? I have statistically evaluated the results of all races for the past month."

They both look at the mathematician whose horse came in first. "How did you do it?"

"Well", he explains. "First, I assumed that all horses were identical and spherical..."

The problems for the exam will be similar to the discussed in the class. Of course, the numbers will be different. But not all of them. Pi will still be 3.14159...

We've all seen this one in many forms, but I particularly like this ending:

A biologist, a statistician, a mathematician and a computer scientist are on a photo-safari in africa. They drive out on the savannah in their jeep, stop and scout the horizon with their binoculars.

The biologist: "Look! There's a herd of zebras! And there, in the middle : A white zebra! It's fantastic! There are white zebra's! We'll be famous!"

The statistician: "It's not significant. We only know there's one white zebra."

The mathematician: "Actually, we only know there exists a zebra, which is white on one side."

The computer scientist: "Oh, no! A special case!"

There was once a very smart horse. Anything that was shown it, it mastered easily, until one day, its teachers tried to teach it about rectangular coordinates and it couldn't understand them. All the horse's acquaintances and friends tried to figure out what was the matter and couldn't. Then a new guy looked at the problem and said,

"Of course he can't do it. Why, you're putting Descartes before the horse!"