econ 2007 solutions

econ 2007 solutions - Economics 120A Dr. Candido Spring...

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Economics 120A – Dr. Candido Spring 2007 Midterm 1 – Solutions Part I: Multiple Choice Version A: 1) a 4) d 7) b 2) b 5) a 8) d 3) c 6) c 9) b Version B: 4) d 4) a 7) b 5) a 5) b 8) a 6) c 6) d 9) c (2 points each; 18 points total) Part II: Problems 1) 300 Employees: 200 computer users; one quarter = .25*300 = 75 Spanish speakers 4/5 of Spanish speakers are computer users Æ (4/5)*75 = 60 employees are both Æ 75 – 60 = 15 employees are Spanish speakers but not computer users Æ 200 – 60 = 140 employees are computer users but not Spanish speakers Æ 300 – (140 + 15 + 60) = 85 employees are neither Computer users only 140 Spanish speakers only 15 Both 60 Neither 85 a) P(Computer and not Spanish) = 140/300 (6 points) b) P(not Computer and not Spanish) = 85/300 (6 points) Note: some students forgot to include the denominator 300 in their answer. The question asks for a probability, so answering 140 or 85 without the denominator is the number of employees with the given characteristics, not the probability.
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2) a) P(F) = 0.23 + 0.43 = 0.66 (6 points) This is the total percentage of the population (both Democrats and non Democrats) that are in favor of stricter gun control laws. b) P(F|D) = P(F and D) / P(D) = 0.23 / (0.23 + 0.06) = 0.23 / 0.29 = 0.793 (5 points) Interpret: This is the percentage of Democrats in favor of stricter gun control. Given that you have chosen a Democrat, the probability that they are in favor of stricter gun control is .793. (3 points) c) No, F is not statistically independent of D. There are two ways to show this: (i) P(F|D) P(F) since P(F|D) = .66 and P(F) = 0.793 (ii) P(F and D) P(F)*P(D) since P(F and D) = .23 and P(F)*P(D) = .66*.29=.19 The intuition behind this answer is that knowing the party affiliation gives insight to the
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This note was uploaded on 05/05/2011 for the course ECON 120A taught by Professor Jeyeon during the Spring '08 term at UCSD.

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econ 2007 solutions - Economics 120A Dr. Candido Spring...

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