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PSY-520 (Statistics)

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Chapter 5, numbers 5.11, 5.13, 5.15, and 5.18 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? First, use the formula for calculating the z-score: X−μ z= σ 125−100 z= 15 25 z= 15 z=1.67 Refer to Table A and find the z-score corresponding to 1.67 for the test scores above 125, which is .0475, so approximately 4.75% would score above Kristen’s 125. (b) below 82? Using the same procedures as above: 82−100 z= 15 −18 z= 15 z=−1.2 The corresponding information found on Table A is .1151 or approximately 11.5% of scores is below 82. (c) within 9 points of the mean?