This couple was having problems with their plumbing. The plumber got under the sink, looked around, then hit an elbow joint as hard as he could with a hammer, and the problem was solved. The couple was overjoyed and asked how much they owed him. The plumber said $75.25.
The couple said, "That's ridiculous. All you did was hit a pipe with a hammer. We want an itemized bill."
So the plumber took out a piece of paper and wrote out $75.25.
.25 cents for wear and tear on the hammer and $75.00 for knowing where to hit the pipe.