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These are the important key points of lecture notes of Introductory Statistics are: Probability Distributions, Bivariate and Multivariate, Number of Contracts, Probability Function, Construction Jobs, Joint Probability Density Function, Random Variables, Proportions, Marginal and Conditional Probability Distributions, Marginal Density
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Stat 366 Lab 3 Problems (September 26, 2006) page 1 TA: Yury Petrachenko, CAB 484, [email protected], http://www.ualberta.ca/∼yuryp/ Bivariate and Multivariate Probability Distributions 5.1 Contracts for two construction jobs are randomly assigned to one or more of three firms, A, B, and C. Let Y 1 denote the number of contracts assigned to firm A, and Y 2 the number of contracts assigned to firm B. Recall that each firm can receive 0, 1, or 2 contracts. (a) Find the joint probability function for Y 1 and Y 2. (b) Find F (1, 0).
5.6 Let Y 1 and Y 2 have the joint probability density function given by
f (y 1 , y 2 ) =
k y 1 y 2 , 0 ≤ y 1 ≤ 1 , 0 ≤ y 2 ≤ 1 , 0 , elsewhere. (a) Find the value of k that makes this a probability density function. (b) Find the joint distribution function for Y 1 and Y 2. (c) Find P (Y 1 ≤ 1 / 2 , Y 2 ≤ 3 /4).
5.12 Suppose that the random variables Y 1 and Y 2 have joint probability density function f (y 1 , y 2 ) given by f (y 1 , y 2 ) =
6 y^21 y 2 , 0 ≤ y 1 ≤ y 2 , y 1 + y 2 ≤ 2 , 0 , elsewhere. (a) Verify that this is a valid joint density function. (b) What is the probability that Y 1 + Y 2 is less than 1?
5.14 Let Y 1 and Y 2 denote the proportions of time (out of one working day) during which employees I and II, respectively, perform their assigned tasks. The joint relative frequency behavior of Y 1 and Y 2 is modeled by the density function
f (y 1 , y 2 ) =
y 1 + y 2 , 0 ≤ y 1 ≤ 1 , 0 ≤ y 2 ≤ 1 , 0 , elsewhere.
Stat 366 Lab 3 Problems (September 26, 2006) page 2 (a) Find P (Y 1 < 1 / 2 , Y 2 > 1 /4). (b) Find P (Y 1 + Y 2 ≤ 1).
Marginal and Conditional Probability Distributions
5.17 Continuing Exercise 5.1.
(a) Find the marginal probability distribution of Y 1. (b) According to results in Chapter 4, Y 1 has a binomial distribution with n = 2 and p = 1/3. Is there any conflict between this result and the answer you provided in (a)?
5.22 Continuing Exercise 5.6.
(a) Find the marginal density functions for Y 1 and Y 2. (b) Find P (Y 1 ≤ 1 / 2 | Y 2 ≥ 3 /4). (c) Find the conditional density function of Y 1 given Y 2 = y 2. (d) Find the conditional density function of Y 2 given Y 1 = y 1. (e) Find P (Y 1 ≤ 3 / 4 | Y 2 = 1/2).
5.28 Continuing Exercise 5.12.
(a) Show that the marginal density of Y 1 is a beta density with α = 3 and β = 2. (b) Derive the marginal density of Y 2. (c) Derive the conditional density of Y 2 given Y 1 = y 1. (d) Find P (Y 2 < 1. 1 | Y 1 = .60).