15-56. The following data are the number of spelling errors detected for every 1000 words on a news Web site over 20 weeks. No. of Spelling No. of Spelling Week Errors Week Errors 3 11 2 12 13 14 15 JOWWACO DO- NWNNUDUON 16 17 18 19 10 20 (a) What control chart is most appropriate for these data? (b) Using all the data. compute trial control limits for the chart in part (a).(Situation P) Below are the results of a survey of America's best graduate and professional schools. The top 25 business schools, as determined by reputation, student selectivity, placement success, and graduation rate, are listed in the table. For each school, three variables were measured: (1) GMAT score for the typical incoming student; (2) student acceptance rate (percentage accepted of all students who applied); and (3) starting salary of the typical graduating student. School GMAT Acc. Rate Salary 1. Harvard 644 15.0% $ 63,000 2. Stanford 665 10.2 60,000 3. Penn 644 19.4 55,000 54.000 4. Northwestern 640 22.6 5. MIT 650 21.3 57,000 6. Chicago 632 30.0 55,269 7. Duke 630 18.2 53,300 8. Dartmouth 649 13.4 52,000 9. Virginia 630 23.0 55.269 10. Michigan 620 32.4 53.300 11. Columbia 635 37.1 52,000 12. Cornell 648 14.9 50,700 13. CMU 630 31.2 52.050 14. UNC 625 15.4 50.800 15. Cal-Berkeley 634 24.7 50,000 16. UCLA 640 20.7 51,494 17. Texas 612 28.1 43.985 18. Indiana 600 29.0 44,119 19. NYU 610 35.0 53.161 20. Purdue 595 26.8 43,500 21. USC 610 31.9 49,080 22. Pittsburgh 605 33.0 43,500 23. Georgetown 617 31.7 45.156 24. Maryland 593 28.1 42,925 25. Rochester 605 35.9 44,499 The academic advisor wants to predict the typical starting salary of a graduate at a top business school using GMAT score of the school as a predictor variable. A simple linear regression of SALARY versus GMAT using the 25 data points in the table are shown below. Bo = -92040 81 = 228 s = 3213 2 = .66 r= .81 df = 23 += 6.67 For the situation above, give a practical interpretation of $ 1 = 228. O We estimate SALARY to increase $228 for every 1-point increase in GMAT. We expect to predict SALARY to within 2(228) = $456 of its true value using GMAT in a straight-line model. O We estimate GMAT to increase 228 points for every $1 increase in SALARY. O The value has no practical interpretation since a GMAT of 228 is nonsensical and outside the range of the sample data.2. (4 points) Let X and Y be jointly continuous RV's with joint PDF fxx (x, y) = - y 0
