25. A survey of the population of 51 students in Psych 311 asks how many credits students are taking and obtains the following normally-distributed results: X= 686 and X2X2= 9832.92. Using this information, answer the following six questions.

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a) What is the mean number of credits that students are enrolled in?(MUST SHOW WORK FOR THIS PROBLEM)

b) Compute the variance (MUST SHOW WORK FOR THIS PROBLEM)

c)Compute the standard deviation (MUST SHOW WORK FOR THIS PROBLEM)

d)What is the percentile rank of a student who is enrolled in 15 credits? (Hint: This is the same thing as asking "what percentage of students is enrolled in 15 credits or less?")MUST SHOW WORK FOR THIS PROBLEM

e) What percentage of students are enrolled in between 12 and 18 credits?(MUST SHOW WORK FOR THIS PROBLEM)

f) What is the 25th percentile? (Hint: This is the same as asking what score separates the bottom 25% of the distribution from the top 75%.)MUST SHOW WORK FOR THIS PROBLEM