Good Riddles

Question: The more of me you have, the longer your life.
The more of me you have, the less you have left.

What am I?

Question: A man finds a small iron coin dated 154 B.C., what's it worth?

Question: I'm number three.
But I'm not a number.
I'm hot and cold at the same moment but not at the same time.
I'm number three.
But I'm not a number.

Who or what am I?

Question: When is 1500 plus 20 and 1600 minus 40 the same thing?

Question:

Take me for a spin and I'll make you cool,
but use me when it's cool and you're a fool.

What am I?