What begins and never ends?

A mathematician, a statistician and an accountant apply for the same job. The interviewer calls in the mathematician and asks "What does two plus two equal?"

The mathematician replies "Four." The interviewer asks "Four, exactly?" The mathematician looks at the interviewer incredulously and says "Yes, four, exactly."

Then the interviewer calls in the statistician and asks the same question "What does two plus two equal?" The statistician says "On average, four - give or take ten percent, but on average, four."

Then the interviewer calls in the accountant and poses the same question "What does two plus two equal?"

The accountant gets up, locks the door, closes the shade, sits down next to the interviewer and says "What do you want it to equal?"