Ch8-NormalDistribution.doc

# Consider a normal distribution with a mean of 25 and

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Consider a normal distribution with a mean of 25 and standard deviation of 4. Approximately, what proportion of the area lies between values of 17 and 33. *a. 95% b. 68% c. 99% d. 50% General Feedback: Answer: A. Because 25±2*4=25±8=17~33, we know that the area is within two standard deviations. Thus, the proportion of the area should be 95%. 8. 8 (1.0 point) Consider a normal distribution with a mean of 10 and standard deviation of 25. What’s the Z score for the value of 35? Correct Answer(s): a. 1 General Feedback: Answer:Z=(35-10)/25=1 9. 9 (1.0 point) For a standard normal distribution, what’s the probability of getting a positive number? *a. 50% b. 95% c. 68% d. We cannot tell from the given information 10. 10 (1.0 point) For a normal distribution with a mean of 16 and standard deviation of 2, what’s the probability of getting a number greater than 20? Correct Answer(s): a. 2.5 b. 2.5% General Feedback: Z=(20-16)/2=4/2=2 , so it is 2.5%

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11. 11 (1.0 point) Fifty students took an Introduction to Chemistry exam. Assume that their scores formed a normal distribution with a mean of 80 and standard deviation of 4. The professor decided to adjust the scores by creating z scores. Only the first 2.5% of students got an A. Students were curious what actual scores would be A’s?
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