Question: 400 university students were surveyed about their long-distance telephone use. The responses were found to be normally distributed. The average monthly long-distance phone usage was 120 minutes, with a standard deviation of 15 minutes.

a) What is the probability that a randomly selected student from this sample uses 100 minutes or more of long-distance phone time?

b) What is the probability that a student uses between 105 and 125 minutes?

c) Would you consider it abnormal for a student to use more than 180 minutes of long-distance phone time in a month? Support your response with calculations.