This is from Dave Coble. It was posted on the groaners listserv.

A prominent Wall Street tycoon, Carmine Intervocalic, wants to hire an M.I.T. computer science graduate student to program the ultimate financial advisor expert system. It turns out that M.I.T. is too expensive, so instead, Carmine hires an undergraduate in applied math from the University of California at Hollywood. After months of programming and millions of dollars of research, the programming is finally done, and Carmine proudly calls up his new toy.

Instantly on the screen:
-> Bank Street Advisor: Ready. Enter command.

Carmine types in:
-> Request: Bank Street Advisor: Compute the secret to success on stock market.

The reply is instantaneous. Crackling on the neon green of the screen is one ominous flashing word: ‘working’.

Carmine is nervous. He paces around. Nothing’s happening. Waits some more. Hum. Nothing’s happening. Waits still more, nothing.

To take his mind off of the wait, Carmine does some business work: Evicting widows and orphans, and so forth.

Well, to make a long story short days pass and, still, all that’s on the screen is “working.”

The program’s sucking in data at a hideous rate, but still no answer. Carmine’s frazzled, and his stocks are plummeting; he’s forced to sell! Sell! Sell!

Carmine is almost broke when finally the answer comes up,
-> Bank Street Writer: Answer computed. Hit space bar.
-> Buy Low. Sell high.

Carmine’s not amused In desperation, he types in,
-> Request: Bank Street Advisor, I need financial advice. What is the best financial advice you can give me? How can I stop wasting money?

The answer’s fast:
-> Sell the computer.

Carmine is plucking out his hair in frenzy. But, he realizes that all he has to do is phrase his requests correctly.
-> Request: How can I predict which stocks will go up in value?

Curiously, the answer doesn’t take long:
-> Make predictions while floating submerged in fizzy apple juice.

Carmine tries it, and it works.

“It works?” his advisors ask.

“Yeah, it works. What? Haven’t you heard of in-cider trading?”