Short Riddles and Answers

Question: When I come in, someone else leaves, I know everyone, yet no one knows me. I'll meet you all only once in your life, Causing mayhem and mischief and sorrowful strife. What am I?

Question: A horse travels a certain distance each day. Strangely enough, two of its legs travel 30 miles each day and the other two legs travel nearly 31 miles. How is this situation possible?

Question: I'm many people's favorite place,
even though many don't remember their stay.
You'll love to come but hate to leave,
if you get cold use my sleeves.

What am I?

Question: My first is often at the front door.
My second is found in the cereal family.
My third is what most people want.
My whole is one of the united states.

What am I?

Question: What do you try to solve. A answer you need to think. To think about with your brain. The brain that's only 10% working. What is it that you try to solve. The question of a lifetime?