Fun Riddles

Question: When you do not know what I am, then I am something. But when you know what I am, then I am nothing. What am I?

Question: A man is twenty years old but has only had five birthdays. How is that possible?

Question: Thirty men and only two women, but they hold the most power.
Dressed in black and white, they could fight for hours.

Who are they?

Question: Mary gets in the shower, but surprisingly her hair is not wet when she gets out. How is this possible?

Question: Four people need to cross a bridge in 17 minutes in the middle of the night. The bridge can only hold two or less people at any time and they only have one flashlight so they must travel together (or alone). The flashlight can only travel with a person so every time it crosses the bridge it must be carried back. Tom can cross in 1 minute, John can cross in 2 minutes, Sally can cross in 5 minutes, and Connor can cross in 10 minutes. If two people cross together they go as fast as the slower person.How can they cross the bridge in 17 minutes or less?