Читать книгу Probability and Statistical Inference - Robert Bartoszynski - Страница 83

We apply here the “classical” definition of probability. The choice of objects without replacement is the same as choosing a subset of objects from the set of total of objects. This can be done in different ways. Since we must have red balls, this choice can be made in ways. Similarly, blue balls can be selected in ways. As each choice of red balls can be combined with each of the choices of blue balls then, by Theorem 3.2.2, the total number of choices is the product and

(3.22)

The next example shows an interesting application of formula (3.22).