SECTION 8.3 Testing the Difference Between Means (Dependent Samples) 443 10. Dow Jones Stocks A stock market analyst claims that the Dow Jones Industrial Average lost value from the closing prices on the previous day to the current prices. The table shows the prices (in dollars per share) of seven randomly selected stocks. At a = 0.01, is there enough evidence to support the analyst’s claim? (Source: Markets Insider) Stock 1 2 3 4 5 6 7 Previous close 199.93 323.26 220.74 136.95 243.22 411.86 279.93 Current price 198.27 318.54 219.32 137.32 244.28 409.95 276.60 11. SAT Scores An instructor for a SAT preparation course claims that the course will improve the test scores of students. The table shows the critical reading scores for 10 students the first two times they took the SAT. Before taking the SAT for the second time, the students took the instructor’s course to try to improve their critical reading SAT scores. At a = 0.01, is there enough evidence to support the instructor’s claim? Student 12345678910 Score (first) 300 450 350 430 300 470 420 370 320 410 Score (second) 400 520 400 490 340 580 450 400 390 450 12. Interval Training A researcher claims that sprint interval training improves running performance in trained athletes. The table shows the maximum aerobic speed (MAS), in kilometers per hour, of trained athletes before and after six sessions of sprint interval training. At a = 0.10, is there enough evidence to support the researcher’s claim? (Adapted from National Strength and Conditioning Association) Athlete 1 2 3 4 5 6 7 8 MAS before training (km/h) 18.5 17.0 12.5 16.5 16.0 13.0 17.5 15 MAS after training (km/h) 18.5 16.5 13.0 16.5 17.5 14.0 18.0 15.5 13. Batting Averages A coach claims that a baseball clinic will help players raise their batting averages. The table shows the batting averages of 14 players before participating in the clinic and two months after participating in the clinic. At a = 0.05, is there enough evidence to support the coach’s claim? Player 1 2 3 4 5 6 7 Batting average (before clinic) 0.290 0.275 0.278 0.310 0.302 0.325 0.256 Batting average (after clinic) 0.295 0.320 0.280 0.300 0.298 0.330 0.260 Player 8 9 10 11 12 13 14 Batting average (before clinic) 0.350 0.380 0.316 0.270 0.300 0.330 0.340 Batting average (after clinic) 0.345 0.380 0.315 0.280 0.282 0.336 0.325
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