Your favorite riddle/paradox?

I've always enjoyed a good riddle or a paradox which get's me thinking.

any good ones?

Post an original if you please ?

 

If a tree falls in a forest, but no ones around to hear it, does it make a sound?

 

How about a math riddle? I didn't make this up, but it's very nice, nonetheless.

"A high school has a strange principal. On the first day, he has his students perform an odd opening day ceremony:

There are one thousand lockers and one thousand students in the school. The principal asks the first student to go to every locker and open it. Then he has the second student go to every second locker and close it. The third goes to every third locker and, if it is closed, he opens it, and if it is open, he closes it. The fourth student does this to every fourth locker, and so on. After the process is completed with the thousandth student, how many lockers are open?"

No Google!

 

A young boy does a paper round every morning, he lives on the 20th floor of his flat, when he goes to do his paper round he goes to ground floor, yet when he returns he goes upto floor 10 and then walks up 10 flights of stairs to his flat, why does he do this?

PM me for answer/think you've got it, you might find on google :s

 

^Because he's too short to reach the button?

 

A cat is placed in a box along with a bomb that has a 50% chance of exploding. There is no way to know if the bomb exploded and killed the cat without opening the box.

You have not opened the box yet.
Is the cat dead or alive?

 

There once was a bitch, she climbed a tree. She was fine as shit, thick as can be. She walked towards me, thighs shakin as she comin. I thought to myself what a spectacular woman. Then shawty.

How many apples does Todd have left?

 

That isn't Schrodinger's cat.

or directly from Schrodinger himself:

While I am a fan of the cat I really do like the Liar's Paradox.