PSY 520 Topic 2 Exercise,Chapter 5 and 8-Latest Solution

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1. Chapter 5, numbers 5.11, 5.13, 5.15, and 5.18 Finding Proportions 5.11 Scores on the Wechsler Adult Intelligence Scale (WAIS) approximate a normal curve with a mean of 100 and a standard deviation of 15. What proportion of IQ scores are: (a) above Kristen’s 125? z= (125-100)/15 = 1.67 P(x>125) = P(z>1.67) = 1-0.9525 = .0475 X 100= 4.75% (b) below 82? Z= 82-100 / 15 = -1.2 Above .1151 X 100 Below: .8849 X 100 (c) within 9 points of the mean? Mean + 9 = 109 – 100 / 15 = .6 Mean – 9 = 91 – 100 / 15 = -.6 .6 = .5239 -.6 = .4761 Answer = .0478 (d) more than 40 points from the mean? 100+40 = 140 140-100 / 15 = 2.66666 = .0039 Finding Scores 5.13 IQ scores on the WAIS test approximate a normal curve with a mean of 100 and a standard deviation of 15. What IQ score is identified with (a) the upper 2 percent, that is, 2 percent to the right (and 98 percent to the left)? X = µ+(z)() Z = x-100/15 = 130.9 = X Z = 2.06 (b) the lower 10 percent? 10% = 10/100 = .1000 Z = -1.28 X = (-1.28x15) + 100 X = 100 + (-19.2) X = 80.8 This study source was downloaded by 100000831988016 from CourseHero.com on 05-02-2022 07:37:10 GMT -05:00 https://www.coursehero.com/file/37524031/Week-2-Execises-1-16-19docx/ (c) the upper 60 percent? .4 = -.25 on chart x= (-.25x15) + 100 X = -3.75 + 100 x= 96.25 (d) the middle 95 percent? [Remember, the middle 95 percent straddles the line perpendicular to the mean (or the 50th percentile), with half of 95 percent, or 47.5 percent, above this line and the remaining 47.5 percent below this line.] 47.5/100 = .475, z = 1.96 X = (1.96 x 15) + 100 X = 29.4 + 100 = 129.4 and X = (-1.96x15) + 100 x = -29.4 +100 x = 70.6 70.6 < x < 129.4 (e) the middle 99 percent? 99/100 = .99 /2 = .495 z= 2.58 X = (2.58x15) + 100 x= 138.7 and x= 100 -(2.58x15) = .61.3 61.36 < X < 138.7 Finding Proportions and Scores IMPORTANT NOTE: When doing Questions 5.15 and 5.16, remember to decide first whether a proportion or a score is to be found. *5. 15 An investigator polls common cold sufferers, asking them to estimate the number of hours of physical discomfort caused by their most recent colds. Assume that their estimates approximate a normal curve with a mean of 83 hours and a standard deviation of 20 hours. (a) What is the estimated number of hours for the shortest-suffering 5 percent? X=μ+(z)(σ ) U = 83 O= 20 83 + -1.64 (20) = 50.2 This study source was downloaded by 100000831988016 from CourseHero.com on 05-02-2022 07:37:10 GMT -05:00 https://www.coursehero.com/file/37524031/Week-2-Execises-1-16

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