Читать книгу Probability and Statistical Inference - Robert Bartoszynski - Страница 61

Either Paul tosses more heads than Peter (event ) or he tosses more tails than Peter (event ). These two events exclude one another and exhaust all possibilities (since one cannot have ties in number of heads and number of tails). Switching the role of heads and tails transforms one of these events into the other. Thus, sample space becomes partitioned into two equiprobable events, and we must have .

The use of (2.7) requires techniques for counting the numbers of elements in some sets. These topics, known under the name combinatorics, will be discussed in Chapter 3.