Logic Riddles

Question: What goes up but never comes down?

Question: In Michigan you cannot take a picture of a man in a green hat.

Why?

Question: There are two boys at an international math contest in December 2013; one is British and one is American. They both write their names, the date, and their answers on the paper. The only problem is that they both have the same name and the papers cannot be told apart.

What is the date?

Question: How can you add 9 to become 6? (No subtracting).

Question: I am a nice word composed of five letters, but the Romans would call me a numbers.

What am I?