As reported in "Runner's World" magazine, the times of the finishers in the New York City 10 km run are normally distributed with a mean of 61 minutes and a standard deviation of 9 minutes. Let x denote finishing time for the finishers.

a) The distribution of the variable x has mean and standard deviation .

b) The distribution of the standardized variable z has mean and standard deviation .

c) The percentage of finishers with times between 40 and 80 minutes is equal to the area under the standard normal curve between and .

d) The percentage of finishers with times exceeding 69 minutes is equal to the area under the standard normal curve that lies to the of .