A sailor came into port with engine trouble. He inspected his engine, made a few unsuccessful attempts to fix it, and finally gave up. He asked the marina to recommend a good mechanic.
When the mechanic arrived he immediately saw the problem, went to his van and came back with a small screw. After installing the screw, he fired up the engine. It ran perfectly. He handed a bill to the owner for two hundred dollars and thirty-five cents.
"What's this?" cried the sailor. "How does a screw cost two hundred dollars?"
"Of course the screw doesn't cost two hundred dollars. The screw only cost thirty-five cents. The two hundred dollars is for knowing where to put it."
-Will