Dear reader,

I need help with a problem which I can not solve. I hope you can help me.

Question:

The time needed to complete a final examination in statistics course is normally

distributed with a mean of 80 minutes and a standard deviation of 10 minutes.

Answer the following questions.

a) What is the probability of completing the exam in one hour or less?

b) What is the probability that a student will complete the exam in more than 60

minutes but less than 75 minutes?

c) Assume that the class has 60 students and that the examination period is 90

minutes in length. Find the probability that 60 randomly selected students

will have a mean time to complete the exam greater than 90 minutes.