Good Riddles

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

Why?

Question: Why did the boy throw the butter out the window?

Question: 8,549,176,320 What makes this number unique?

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: You went into the forest and got me,
you sat down to find me,
you went home with me because you couldn't find me.

What am I?