Good Riddles

Question: Two criminals, Rob and Stan, are thrown into jail. But they plan to escape. There is a open window twenty feet off the ground. They try and try but are never able to reach it. They decide to dig their way out instead. After months of digging, they come up with a much easier plan. The plan works and they escape.

What was the plan?

Question: You have a cube made of 10 x 10 x 10 smaller cubes, for a total of 1000 smaller cubes. If you take off 1 layer of cubes, how many remain?

Question: You have two buckets: one with only white marbles and one with only black marbles. The two buckets have the same number of marbles.

How can you rearrange the marbles to maximize your chances of grabbing a white marble from each?

Question: I am a digit, but two of the ten.
Two of me make a promise.

What am I?

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?