Imagine you are in a dark room with a locked door. All you have with you is a rope and a pencil. You can hear the rain outside, but there
are no windows. How do you get out?
Look in the mirror, then at the wall and back at the mirror to see what you saw. Use the saw to cut the table in half and join the two halves to make a whole. Put the “hole” on the wall and climb out.
I know, it’s lame. I like to have brain teasers that you can realistically guess, but this one’s so popular, I feel an obligation to include it.