Exam-1-Universe-Ch3-A

# Exam-1-Universe-Ch3-A - BUS-271 Exam-1 Universe Answers...

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1 BUS-271 Exam-1 Universe Answers 2011-08-31 CHAPTER 3 301. [Ch. 3; 28 points] (Descriptive statistics) We want to examine whether there is any relationship between the number of times a student has attended class, and their average grades going into the final. Our data set is as follows: X = number of class meetings attended (out of 18) Y = average grade on exams taken I x i y i --- --- ------- 1 18 103.7 2 18 95.0 3 18 89.0 4 18 79.7 5 18 75.3 6 18 73.3 7 18 66.3 8 17 77.0 9 17 59.7 10 15 82.3 11 15 68.7 12 15 67.3 13 15 66.7 14 15 65.3 15 14 70.7 16 13 93.0 17 13 76.0 18 10 63.0 19 9 57.0 20 8 59.0 21 6 92.0 22 6 77.0 23 6 71.0 24 3 0.0 25 2 0.0 26 2 0.0

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2 First, USING OBSERVATIONS NUMBER 7 THROUGH 11 ONLY, calculate the following sums: a. [2 p.] X 16.4 b. [2 p.] Y 70.8 c. [2 p.] 11 7 i i x 82.0 d. [2 p.] 11 7 i i y 354.0 e. [2 p.] 11 7 () i i xx  0 (always, if your calculations are correct) f. [2 p.] 11 7 ii i xy  5,782.3 (NOT equal to i i y x  !) g. [2 p.] 11 7 ( ) ( ) i x X y Y -23.3 (NOT equal to ( ) ( ) i i XY y x !)
3 Next, USING THE WHOLE DATA SET, the following pre-calculated sums are provided for your use: 2 2 2 4,875.00 ( ) 0 ( ) 762.35 ( ) 0 ( ) 18,429.74 24,301.60 ( ) ( ) 2,568.68 i i i i i ii x xX yY xy x X y Y   Using this information: h. [6 p.] Calculate the co-variance s xy and the standard deviations s x and s y : 2 2 762.35 5.52 1 26 1 () xx i n X x ss  2 2 18,429.74 27.15 1 26 1 yy i n Y y ( )( ) 2,568.68 102.75 1 26 1 i i xy XY n y x s i. [4 p.] Calculate the Pearson Correlation Coefficient r xy 102.75 0.6856 5.52 27.15 xy xy s r 

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4 j. [4 p.] What do the covariance and correlation coefficients you just calculated tell us about the relationship between x and y in this data set?
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Exam-1-Universe-Ch3-A - BUS-271 Exam-1 Universe Answers...

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