A boy goes to his father one day: "What's the difference between theoretically and realistically?"
His father says: "Ask your mum whether she'd sleep with the milkman for £1million."
So the child goes to ask his mother the question. She replies: "Yes, of course."
So the boy goes and tells his dad. The father then tells his son to go and ask his sister if she would sleep with the coal man for £2 million.
So he goes away and asks his sister who replies: "Yes, of course I would!"
Still confused by what on Earth this has to do with his original question, the boy returns to his father and tells him what his sister said.
"Well there's your answer then boy!" Says the father. "Theoretically, we're sitting on £3 million. Realistically, we're living with two sluts!"