Exam 2 - 1 Suppose z is a standard normal variable and...

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1. Suppose z is a standard normal variable and using Table A1: What is the relative frequency of observations from z greater than -.58 ? P(Z > -0.58) = 1 – P(Z < -0.58) = 1 – 0.2810 = 0.7190 What is the relative frequency of observations from z between -1.0 and 1.0 ? P(-1.0 < Z < 1.0) = P(Z < 1.0) - P(Z < -1.0) = 0.8413 – 0.1587 = 0.6826 What is the eightieth percentile of z ? [That is, find the value such that approximately 80% of the standard normal observations fall below z .] Z = 0.84 from the table find the 4-digit probability closest to 0.8000 What is the first quartile, Q1, of z ? [That is, find Q1 such that the relative frequency of observations from z falling below Q1 is approximately .2500] Z = – 0.67 from the table find the 4-digit probability closest to 0.2500 2. The Chapin Social Insight Test evaluates how accurately the subject appraises other people. In the reference population used to develop the test, scores were approximately normally distributed with mean 25 and standard deviation 5. The range of possible scores is 0 to 41. What proportion of the population has scores below 20 on the Chapin test?
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