433. Gifted Paintings. A wealthy collector had 10 valuable paintings. He wanted to make a gift to a museum, but the collector couldn't figure out how many gift options he had: after all, he could give any one painting, any two, any three paintings, and so on, he could even give all ten paintings.

The reader might think that answering this question would require a long and tedious calculation; however, I will provide a small rule that allows one to answer in all similar cases without any difficulties and thankless work.