Midterm Exam 2 Practice Problems  Econometrics 120A
1. Consider the following fictional joint distribution of the color of car driven and the number of speeding
tickets received per year.
Car Color / Tickets per year
0 Tickets
1 Ticket
2 Tickets
White
1/10
1/10
0
Red
0
1/10
3/10
Blue
1/10
2/10
1/10
(a) What is the probability of receiving 0 tickets? What is the probability of getting 1 ticket? What
is the probability of getting 2 tickets?
(b) What is the probability of driving a red car conditional on having received 2 tickets? What is
the probability of driving a red car conditional on having received no tickets?
(c) Are the number of tickets received and the color of the car independent?
(d) What is the mean of the number of tickets? What is the variance of the number of tickets?
(e) Does the concept of covariance make sense in this context? Justify your answer.
2. The true proportion of Democrats is 0.45, while the proportion of Republicans is 0.55. Suppose you
poll 5 people, and let
X
i
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 Spring '10
 Elliot
 Probability, Probability theory, Tickets

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