Suppose the scores on a statistic exam are normally distributed with a mean of 77 and...
Suppose the scores on a statistic exam are normally distributed with a mean of 77 and a variance of 25.
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What is the 25th percentile of the scores?
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What is the percentile of someone who got a score of 62?
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What proportion of the scores are between 80 and 90?
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Suppose you select 35 tests at random, what is the proportion of scores above 85?
Homework Answers
Let X be the score on that statistic exam.Then X~ N(77,25)
1.25th percentile of the population is 25th percentile of N(77,25) which is 73.627
2. percentile for 62 is P(X<=62) *100 = 0.0013 *100 = 0.13th percentile
3. required answer is P(80<=X<=90) = 0.2696
4. the proportion will be same as P(X>85)*100 = 0.0548*100 = 5.48%
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