Homework Set - Module 7

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Utah State University *

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Economics

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Apr 3, 2024

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Gloria Hansen Homework Set – Module 7 3.30) Suppose P(A) = .4, P(B) = .7, and P(A Ç B) = .3. Find the following probabiliBes: a) P(B c ) .7 + P(B c ) = 1 1 - .7 = .3 b) P(A c ) .4 + P(A c ) = 1 1 - .4 = .6 c) P(A È B) .4 + .7 - .3 = .8 3.31) A fair coin is tossed three Bmes, and the events A and B are defined as follows: A: {At least one head is observed.} B: {The number of heads observed is odd} a) IdenBfy the sample points in the events A, B, A È B, A c , and A Ç B. a. A = {HTT, THT, TTH, HHT, HTH, THH, HHH} b. B= {HTT, THT, TTH, HHH} c. A È B = {HTT, THT, TTH, HHT, HTH, THH, HHH} d. A c = {TTT} e. A Ç B = {HTT, THT, TTH, HHH} b) Find P(A), P(B), P(A È B), P(A c ), and P(A Ç B) by summing the probabiliBes of the appropriate sample points. a. P(A) = 1/8 * 7 = 7/8 = .875 b. P(B) = 1/8 * 4 = 4/8 = .5 c. P(A È B) = 1/8 * 7 = .875 d. P(A c ) = 1 - .875 = .125 e. P(A Ç B) = 1/8 * 4 = 4/8 = .5 c) Find P(A È B) using the addiBve rule. Compare your answer with one you obtained in part b. P(A È B) = P(A) + P(B) - P(A Ç B) P(A È B) = .875 + .5 - .5 = .875 I got the same answer as before. d) Are events A and B mutually exclusive? Why? No. Both events can happen simultaneously. 3.34) Consider the Venn diagram in the next column, where P(E1) = .10, P(E2) = .05, P(E3) = P(E4) = .2, P(E5) = .06, P(E6) = .3, P(E7) = .06, and P(E8) = .03. Find the following probabiliBes: a) P(A c ) P(E3) + P(E6) + P(E8) .20 + .30 + .03 = .53
Gloria Hansen b) P(B c ) P(E1) + P(E7) + P(E8) .10 + .06 + .03 = .19 c) P(A c Ç B) P(E3) + P(E6) .20 + .30 = .5 d) P(A È B) P(E1) + P(E7) + P(E2) + P(E4) + P(E5) + P(E3) + P(E6) 1 - .03 = .97 .10 + .06 + .05 + .20 + .06 + .20 + .30 = .97 e) P(A Ç B) P(E2) + P(E4) + P(E5) .05 + .20 + .06 = .31 f) P(A c Ç B c ) P(E8) = .03 g) Are events A and B mutually exclusive? Why? No. Both events can happen simultaneously. 3.39) The Journal of AccounBng Research (March 2008) published a study on relaBonship incenBves and degree of opBmism among analysts’ forecasts. ParBcipants were analysts at either a large or small brokerage firm who made their forecasts either early or late in the quarter. Also, some analysts were only concerned with making an accurate forecast, while others were also interested in their relaBonship with management. Suppose one of these analysts is randomly selected. Consider the following events: A = {The analyst is concerned only with making an accurate forecast.} B = {The analyst makes the forecast early in the quarter.} C = {The analyst is from a small brokerage firm.} Describe each of the following events in terms of unions, intersecBons, and complements (e.g., A È B, A Ç B, A c , etc.). a) The analyst makes an early forecast and is concerned only with accuracy. A Ç B b) The analyst is not concerned only with accuracy. A c c) The analyst is from a small brokerage firm or makes an early forecast. B È C d) The analyst makes a late forecast and is not concerned only with accuracy. A c Ç B c 3.42) In the United States, Facebook is the most popular social networking Web site. Another popular social network is Twiger. According to a 2019 Pew Internet Research survey of 1,052 adults, 69% use Facebook and 22% use Twiger. Assume that these are Facebook only and Twiger only users. Also, assume that 10% use both Facebook and Twiger.
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