Good Riddles

Question: A man was found dead in his study. He was slumped over his desk and a gun was in his hand. There was a cassette recorder on his desk. When the police entered the room and pressed the play button on the tape recorder they heard: "I can't go on. I have nothing to live for." Then there was the sound of a gunshot. How did the detective immediately know that the man had been murdered and it wasn't a suicide?

Question: If a white house is white and a yellow house is yellow, what color is a green house?

Question: Whoever makes it, tells it not. Whoever takes it, knows it not. Whoever knows it, wants it not.

What is it?

Question: Sum Sam and Product Pete are in class when their teacher gives Sam the Sum of two numbers and Pete the product of the same two numbers (these numbers are greater than or equal to 2). They must figure out the two numbers.

Sam: I don't know what the numbers are Pete.
Pete: I knew you didn't know the numbers... But neither do I.
Sam: In that case, I do know the numbers.

What are the numbers?

Question: The more you take, the more you leave behind.
What are they?