As an example consider an experiment with two outcomes, H & T. The first sample space has two points and each has a probability of p(T) and p(H). Suppose we repeat the process twice, two experiments, considered as one event: (TT), (TH), (HT), (HH). Assuming independence then the probability of each of these events can be calculated. Suppose I want to consider the event (TT)(HH) to be a new event. Then the new sample space will have all possible pairs of (XY) where X and Y are the pairs (TT), (TH), (HT), (HH). There will be 16 events each with a probability you can calculate assuming independence. Now I wish to consider a new set of events that are made up of three of the (XY) events. For example {(TT)(TH); (TT)(HH); (TT)(TH)} now there are (16)^3 events. What is the probability there are 7 T's and 5 H's in these events?