Find the Next Number in the Sequence

2 9 3 1 8 4 3 6 5 7 ?

A woman is sitting in her hotel room and hears a knock at the door. She opens the door to see a man whom she’s never met before. He says, “I’m sorry, I have made a mistake, I thought this was my room.” He then goes down the corridor and into the elevator. The woman goes back into her room and calls security. What made the woman so suspicious of the man?

How can you throw a ball as hard as you can and have it come back to you even if it doesn't hit anything there is nothing attached to it and no one else catches or throws it.

I can write cow in 13 letters.

Can You?

There's one "sport" in which neither the spectators nor the participants know the score or the leader until the contest ends.

What is it?

How can one talk without saying a single word?

Find The Next Number in the series:

12 13 15 17 111 113 117 119 123 ?

Look at this sequence from top to bottom. What is the next number in the sequence?
1
11
21
1211
111221
312211

What can run but never walk, have a mouth that never speaks, have a head that never weeps, and have a bed but never sleeps?

Before Mount Everest was discovered, what was the highest mountain in the world?