Statistical Jokes 2

A biologist, a statistician and a mathematician are sitting outside a cafe watching the world go by. A man and a woman enter a building across the road. Ten minutes later, they come out accompanied by a child.

"They've reproduced," says the biologist.

"No," says the statistician. "It's an observational error. On average, two and a half people went each way."

"No, no, no," says the mathematician. "It's perfectly obvious. If someone goes in now, the building will be empty."