Maria.M

A ship engine failed and no one could fix it, so they brought in a Mechanical Engineer with 40 years experience.
He inspected the engine very carefully, top to bottom.
After looking things over, the guy reached into his bag and pulled out a small hammer.
He gently tapped something. Instantly, the engine burst back into life.
The engine was fixed!
7 Days later the owners got his bill for $10,000.
"What?!" the owners said. "You hardly did anything. Send us an itemized bill."
The reply simply said:
Tapping with a hammer: $2
Knowing where to tap & how much forcefully to tap: $9,998