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20-hw3-students - Stat 20 solutions to homework 3 Michael...

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Stat 20: solutions to homework 3 Michael Lugo September 21, 2010 Chapter 8: review problems 5, 8, 9, 11. Chapter 9: review problems 2, 5, 9, 11, 12 Chapter 8, # 5 Answers: (i) 0.60, (ii) 0.30, (iii) 0.95. All three of these correlations should be positive – good students in freshman year tend to remain good students later, and a longer two-by-four will of course be heavier. The correlation of the length of two-by-fours with their weight should be very high – the weight of a two-by-four is very close to being a constant multiple of its length. The GPA correlations are the two other positive ones. The courses students take in their freshman year are more similar to those they take in their sophomore year than to those they take in their senior year, so the GPAs should be similar. Chapter 8, # 8 (a) 42 inches - for these sorts of distribution the average will be very close to where the most dots are. (b) 2.5 inches. The mean is around 71; we expect to see points perhaps two standard deviations from the mean, which we do. If the standard devia-
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