exam1_answer_econ120a_su05

exam1_answer_econ120a_su05 - Economics 120A July 18, 2005...

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Economics 120A Name: _________________________ July 18, 2005 Student ID#: _____________________ Answer to Midterm Exam: Econometrics (Econ 120A) 1-a. (3 points) The probability of an event A or B (Pr( A B )) to occur equals a. Pr( A ) × Pr( B ). b. Pr( A ) + Pr( B ) if A and B are mutually exclusive. c. Pr( ) Pr( ) A B . d. Pr( A ) + Pr( B ) even if A and B are not mutually exclusive. Answer : b 1-b. (3 points) The cumulative probability distribution shows the probability a. that a random variable is less than or equal to a particular value. b. of two or more events occurring at once. c. of all possible events occurring. d. that a random variable takes on a particular value given that another event has happened. Answer : a 1-c. (3 points) Let Y be a random variable. Then var( Y ) equals a. 2 [( ) ] Y EY µ . b. [|( ) |] Y . c. 2 [( ) ] Y . d. [( )] Y . Answer : c 1-d. (3 points) The correlation between X and Y a. cannot be negative since variances are always positive. b. is the covariance squared. c. can be calculated by dividing the covariance between X and Y by the product of the two standard deviations. d. is given by cov( , ) (,) var( ) var( ) XY corr X Y X Y = . Answer : c
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2 Answer to MIDTERM EXAM, ECON 120A, SUMMER 2005 1-e. (3 points) var( ) aX bY += a. 22 XY ab σ + . b. 2 XX Y Y aa b b σσ ++ . c. XY X Y µµ + . d. + . where 2 x is the variance of X and xy is the covariance of X and Y . Answer : b 2. (10 points) A sample of twelve Econ120A students found the following figures for number of hours spent studying the course material in the week before the final exam: 12 7 4 16 21 5 9 3 11 14 10 6 (a) (2 points) Find the sample mean. (b) (3 points) Find the sample median (c) (3 points) Find the sample variance and standard deviation (d) (2 points) Find the interquartile range (answer) (a) 8333 . 9 12 118 = = = n x x i (b) median = (9+10)/2=9.5 (c) 5152 . 28 11 333 . 1160 1474 2 = = s and s=5.34 (d) 1 st quartile = 5+(1/4)=5.25 3 rd quartile = 12+(3/4)(14-12)=13.5 interquartile range = 8.25
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3 Answer to MIDTERM EXAM, ECON 120A, SUMMER 2005 3 . (10 points)
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This note was uploaded on 08/29/2008 for the course ECON 120A taught by Professor Jeyeon during the Spring '08 term at UCSD.

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exam1_answer_econ120a_su05 - Economics 120A July 18, 2005...

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