One day a man walks into a dentist's and asks how much it will cost to extract wisdom teeth?
"$160," the dentist says.
"That's a ridiculous amount," the man says. "Isn't there a cheaper way?"
"Well," the dentist says, "if you don't use an anaesthetic, I can knock it down to $120."
"That's still too expensive," the man says.
"Okay," says the dentist. "If I save on anaesthesia and simply rip the teeth out with a pair of pliers, I could get away with charging $40."
"Nope," moans the man, "it's still too much."
"Hmm," says the dentist, scratching his head. "If I let one of my students do it for the experience, I suppose I could charge you just $20."
"Marvellous," says the man, "book my wife for next Tuesday !"