# Question

A certain unnamed statistics teacher needs to grade 90 exams. The teacher claims that exams require an average of 12 minutes to grade with a standard deviation of 3 minutes. A random sample of 15 exams is selected.

a. What is the probability that the sample mean will be more than 11 minutes per exam?

b. What is the probability that the sample mean will be more than 12.5 minutes per exam?

c. Suppose the sample mean is 10 minutes. Is the teacher’s claim valid according to this sample?

d. What assumptions need to be made in this problem?

a. What is the probability that the sample mean will be more than 11 minutes per exam?

b. What is the probability that the sample mean will be more than 12.5 minutes per exam?

c. Suppose the sample mean is 10 minutes. Is the teacher’s claim valid according to this sample?

d. What assumptions need to be made in this problem?

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