# midtermS03_answer - Economics 120A Name_key Student ID...

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Economics 120A Name: ________key_________________ July 14, 2003 Student ID#: _________________________ ANSWER to Midterm Exam: Econometrics 1. (10 points) An investment councilor recently reviewed the account activity of 10 of his clients. He was interested in the average number of stock trades per month over the past year. He collected the following data: 10.2 2.5 11.4 3.2 1.1 3.4 8.4 9.7 11.2 2.4 a.) Calculate the average number of trades per month for these 10 clients. (Answer) Mean = 6.35. b.) Calculate the standard deviation. (Answer) Standard deviation = 4.16. 2. (10 points) A recent survey asked respondents about their monthly purchases of lottery tickets. Below are the monthly expenditures, in dollars, of ten people who play the lottery. What can we say about the shape of the distribution? 23 15 11 20 28 31 13 10 20 24 a.) Skewed to the left. b.) Skewed to the right. c.) Approximately mound-shaped. d.) Skewed to the left and the right. (Answer) A

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2 MIDTERM EXAM, ECON 120A, SUMMER 2003 3. (20 points) A recent survey of 200 top executives asked how many hours they spend each year in community service. The data from this survey is presented below. # of Hours 0<20 20<40 40<60 60<80 80<100 100<120 120<140 # of Executives 11 27 33 53 47 22 7 3-a. What is the estimated mean amount of time spent by these executives in community service? (Answer) Midpoint frequency m*f m*m*f 10 11 110 1100 30 27 810 24300 50 33 1650 82500 70 53 3710 259700 90 47 4230 380700 110 22 2420 266200 130 7 910 118300 Sum 200 13840 1132800 The sample mean is 2 . 69 200 13840 7 = = = = n m f X i i i i . 3-b. What is the estimated standard deviation for this data? (Answer) The sample variance is [] 76 . 879 1 200 2 . 69 * 200 1132800 1 2 7 2 2 2 = = = = n X n m f s i i i i . Thus the sample standard deviation is 66 . 29 2 = = s s .
3 MIDTERM EXAM, ECON 120A, SUMMER 2003 4.

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midtermS03_answer - Economics 120A Name_key Student ID...

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