 # Statistics Problems

## Question

Instructions for Exercises 12.2 (a) Make an Excel scatter plot. What does it suggest about the population correlation between X and Y? (b) Make an Excel worksheet to calculate SSxx , SSyy , and SSxy . Use these sums to calculate the sample correlation coefficient. Check your work by using Excel’s function =CORREL(array1,array2). (c) Use Appendix D to find t.05 for a two-tailed test for zero correlation.

(d) Calculate the t test statistic. Can you reject ρ = 0? (e) Use Excel’s function =TDIST(t,deg_freedom,tails) to calculate the two-tail p-value.

12.2 Part-Time Weekly Earnings (\$) by College Students

Hours Worked (X) Weekly Pay (Y)
10 93
15 171
20 204
20 156
35 261

Instructions for Exercises 12.4–12.6: (a) Make a scatter plot of the data. What does it suggest about the correlation between X and Y? (b) Use Excel, MegaStat, or MINITAB to calculate the correlation coefficient.

(c) Use Excel or Appendix D to find t.05 for a two-tailed test. (d) Calculate the t test statistic.
(e) Calculate the critical value of rα. (f) Can you reject ρ = 0?

12.4 Moviegoer Spending (\$) on Snacks

Age (X) Spent (Y)
30 2.85
50 6.50
34 1.50
12 6.35
37 6.20
33 6.75
36 3.60
26 6.10
18 8.35
46 4.35

12.6 Number of Orders and Shipping Cost (\$)

Orders (X) Ship Cost (Y)

1,068 4,489
1,026 5,611
767 3,290
885 4,113
1,156 4,883
1,146 5,425
892 4,414
938 5,506
769 3,346
677 3,673
1,174 6,542
1,009 5,088

12.8 (a) Interpret the slope of the fitted regression Sales = 842 − 37.5 Price. (b) If Price = 20, what is the prediction for Sales? (c) Would the intercept be meaningful if this regression represents DVD sales at Blockbuster?

12.10 The regression equation NetIncome = 2,277 + .0307 Revenue was fitted from a sample of 100 leading world companies (variables are in millions of dollars). (a) Interpret the slope. (b) Is the intercept meaningful? Explain. (c) Make a prediction of NetIncome when Revenue = 1,000.

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