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Unformatted text preview: Homework 4 (STAT515, Fall 2011) 2.110 ( 4 points ) According to the provided statistics, the average scores is 279, 25% of the eighth graders scored lower than 255, 75% lower than 304, and 10% higher than or equal to 324 (i.e., 90% below 324). 2.114. ( 4 points ) The water customers in my subdivision are not at risk of drinking water with unhealthy lead levels. Because the 90th percentile of the sample from this subdivision had a lead concentration of 0.00372 mg/L, which indicates that 90% of the sample had lead level no more than 0.00372 mg/L. Therefore more than 90% of the sample had lead level lower than 0.015 mg/L (the EPA Action Level ). 2.117. ( 16 points ) Suppose that all the students in this university form a population. It is given that the population mean GPA is = 2 . 7 and the population standard deviation of GPA is = 0 . 5. a. ( 8 points ) The relationship between the value of GPA ( x ) and the associated z-score is given by x = + z . Based on this relationship, one can convert the....
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