An electrician was called to a man's house that was having electrical problems. The electrician examined the wiring, looking, poking around, then pulled out a wire and replaced it. Suddenly everything was working perfectly.

The electrician told the man "that'll be $80".

The man looked at him and exclaimed "$80??!! All you did was change out a cheap wire!"

The electrician paused a minute, then said "Well, the wire only cost 24 cents. But the $79.76 was for knowing which wire it was."