IPS6e.ISM.Ch02

IPS6e.ISM.Ch02 - Chapter 2 Solutions 2.1. The individuals...

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Chapter 2 Solutions 2.1. The individuals are students. 2.2. With this change, the cases are dog breeds; the variables (both quantitative) are breed size and average life span. 2.3. With this change, the cases are cups of Mocha Frappuccino (as before). The variables (both quantitative) are size and price. 2.4. Size seems to be the most reasonable choice for explanatory variable because it seems nearly certain that Starbucks ±rst de- cided which sizes to offer, then determined the appropriate price for each size (rather than vice versa). The scatterplot shows a positive association between size and price. 3.00 3.20 3.40 3.60 3.80 4.00 4.20 10 12 14 16 18 20 22 24 Cost ($) Size (ounces) 2.5. (a) “Month” (the passage of time) explains changes in temperature (not vice versa). (b) Temperature increases linearly with time (about 10 degrees per month); the relationship is strong. X X X X February March April May 25 30 35 40 45 50 55 60 Temperature (degrees F) Month 2.6. (a) First test score should be explanatory since it comes ±rst chronologically. (b) The scatterplot shows no clear association; however, the removal of one point (the sixth student, in the upper left corner of the scatterplot) leaves a weak-to-moderate positive association. (c) A few students can disrupt the pattern quite a bit; for example, perhaps the sixth student studied very hard after scoring so low on the ±rst test, while some of those who did extremely well on the ±rst exam became overcon±dent and did not study hard enough for the ±nal (the points in the lower right corner of the scatterplot). 140 145 150 155 160 165 170 175 115 120 125 130 135 140 145 150 155 160 Final exam score First test score 90
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Solutions 91 2.7. (a) The second test happens before the Fnal exam, so that score should be viewed as ex- planatory. (b) The scatterplot shows a weak positive association. (c) Students’ study habits are more established by the middle of the term. 140 145 150 155 160 165 170 175 135 140 145 150 155 160 165 170 175 Final exam score Second test score 2.8. To be considered an outlier, the point for the ninth student should be in either the upper left or lower right portion of the scatterplot. The former would correspond to a student who had a below-average second-test score but an above-average Fnal-exam score. The latter would be a student who did well on the second test but poorly on the Fnal. 2.9. (a) Age is explanatory; weight is the response variable. (b) Explore the relationship; there is no reason to view one or the other as explanatory. (c) Number of bedrooms is explanatory; price is the response variable. (d) Amount of sugar is explanatory; sweetness is the response variable. (e) Explore the relationship. 2.10. Parents’ income is explanatory, and college debt is the response. Both variables are quantitative. We would expect a negative association: Low income goes with high debt, high income with low debt. 2.11. (a) In general, we expect more intelligent children to be better readers and less intelligent children to be weaker. The plot does show this positive association. (b) The four points are for children who have moderate IQs but poor reading scores. (c) The rest of the scatterplot
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IPS6e.ISM.Ch02 - Chapter 2 Solutions 2.1. The individuals...

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