Wayne QuickLube management has recently begun a quality improvement effort. One project in this effort is related to service time for oil-change customers. Wayne promises customers that a standard oil change service will be completed in 20 minutes or less. Data Wayne has collected over the past year indicate that the time for a standard oil change service is approximately normally distributed, with a mean of 14.0 minutes and a standard deviation of 3.5 minutes. Although Wayne promises customers that their standard oil change will be completed in 20 minutes or less, they strive to delight their customers, so their internal goal is actually to complete as many of the oil changes as possible in under 15 minutes. 

1. What is the probability that an oil change will be completed within the following time ranges (assuming that the distribution of oil change times has not changed from what it was in the past year)? 

a. less than 20 minutes? 

b. less than 15 minutes? 

c. more than 15 minutes? 

d. between 14 and 16 minutes?