### Instruction: Alyssa has four marbles: a red one, a blue one, a green one, and a yellow one. In how many different ways can she form a set consisting of some of the marbles if she must choose at least one marble?  (In a set of chosen marbles, it does not matter in what order she chose the marbles.).### Response: I need to count the number of subsets of the set of four marbles, excluding the empty subset.
I recall that the number of subsets of a set with n elements is 2^n, since for each element I have two choices: include it or not.
So the number of subsets of the set of four marbles is 2^4 = 16.
However, this includes the empty subset, which I need to exclude.