# Ch. 5 discrete probability distributions problems 13 and 17

Need help with problems 13 and 17. Please use excel and different worksheets per problem.

Ch. 5 is a super easy chapter. It shows us what the probability distributions are for discrete random variables (says, the number of TV’s or computers sold; it can be X=0, 1, 2, 3, 4, or 5 with different probabilities, see Table 5.4 on P. 234). The chapter then shows us how to find the average value, variance, and the s.d. of the random variable. For instance, later in this chapter, it shows us how to find the average number of TV’s sold, says 1.5 units shown in Table 5.5 on P. 239, and the variance of the number of TV’s sold at 1.25 units in Table 5.6 on P. 239.

That is it. Three major concepts to know:

(1) What is the valid probability distribution — “two” conditions (you have to check “two” conditions, not only “one” condition) on P. 234. There’s no stats function for it.

(2) Manually find the expected value of X, E(X) by equation (5.4) on P. 238, and its Excel Spreadsheet calculation is shown in Table 5.5 on P. 239. Excel Stats function is shown in Figure 5.2 through =sumproduct on P. 240.

(3) Manually find the variance of X, Var(X) by equation (5.5) on P. 239, and its Excel Spreadsheet calculation is shown in Table 5.6 on P. 239. Excel Stats function is shown in Figure 5.2 through =sumproduct on P. 240.

(4) To learn more about “Discrete Random Variable”, we will discuss the “5.5 Binomial Probability Distribution” on pp. 254-265 in the DB. The stats function to find the probability for a binomial distribution, P(X=x), is binor.dist(x, n, p, false). The stats function to find the cumulative probability for a binomial distribution, P(X<=x), is binor.dist(x, n, p, true).

If you have any questions from Ch. 5, please feel free to post your questions for a discussion in the thread titled “Any Other Questions you have from Ch. 5” in this page.