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: What is 1/2 of 2/3 of 3/4 of 4/5 of 5/6 of 6/7 of 7/8 of 8/9 of 9/10 of 10,000?