# 2012_final - Final Exam Instructor Tessa Childers-Day Stat...

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Stat 20Final ExamInstructor: Tessa Childers-Day9 August 2012Please write your name and student ID below, and circle your section. With yoursignature, you certify that you have not observed poor or dishonest conduct on the part ofyour classmates. You also certify that you have not been a party to poor or dishonestconduct, and that the work on this exam is solely your own.Name:Student ID:Signature:Date:Section:101 (2pm-3pm)102 (3pm-4pm)Answer the questions in the spaces provided. There are questions on the front and back ofeach page. This exam has 9 questions, for a total of 60 points and 6 bonus points.Thisfinal is cumulative. Show your work, including labeling quantities (such as z-scores). Theclearer that your work is, the easier it is to award partial or full credit. If you do not showyour work, you will not receive credit. You are welcome to leave your answers as fractions.If you use decimals, please round all answers to two significant figures, and hold yourrounding until the final calculation.QuestionPointsScore19273448586579810Bonus0Total:60
Stat 20Final Exam, Page 2 of 149 August 20121. Measurements of the water salinity in Pamlico Sound, North Carolina were recorded between March andMay in the springs of five consecutive years. The observations came two weeks apart. That is, the firstsalinity measurement was made, and then two weeks later, another observation was made. The salinityis measured in Parts per Thousand (ppt). A scatterplot of the relationship is shown below, along withmeans, SDs, and the correlation coefficient. Assume that the scatterplot is “football shaped”, and thusthat the first and second observations have approximately normal histograms.468101214468101214Salinity Measurement of Pamlico Soundin Parts Per Thousand (ppt)First Measurement (ppt)Second Measurement (ppt)First Measurement: mean = 10.33 pptsd = 3.04 pptSecond Measurement: mean = 10.55 pptsd = 2.96 pptcorrelation: r = 0.87(a) (2 points) Suppose that I traveled to Pamlico Sound in April, and observed a salinity measurementof 12 ppt. When I returned two weeks later, what salinity measurement did I expect to see? (Includeunits and round your answer to two decimal places)
Stat 20Final Exam, Page 3 of 149 August 2012(b) (2 points) About how far off did I expect my prediction in part (a) to be? (Include units and roundyour answer to two decimal places)(c) (3 points) Say that I observed the first salinity measurement of 12 ppt. What is the chance thatmy second salinity measurement is between 12.5 ppt and 15 ppt?(d) (2 points) Say that I return in December, and observe a salinity measurement of 28 ppt. I then usethe regression method to predict that my salinity measurement two weeks later will be 25.52 ppt.Do you agree with what I have done? Why or why not?
Stat 20Final Exam, Page 4 of 149 August 2012