Suppose the average speeds of passenger trains traveling from Newark, New Jersey, to Philadelphia, Pennsylvania, are normally distributed, with a mean average speed of 88 miles per hour and a standard deviation of 6.4 miles per hour.
a. What is the probability that a train will average less than 70 miles per hour?
b. What is the probability that a train will average more than 80 miles per hour?
c. What is the probability that a train will average between 90 and 100 miles per hour?