During 2004, the average number of flying hours for aircraft operated by regional airlines in the United States was 2389. Assume a normal distribution and a standard deviation of 300 hours. Source: Statistical Abstract of the United States 2006, p. 701.
a. What proportion of aircraft flew more than 2200 hours during the year?
b. What proportion of aircraft flew between 2000 and 2400 hours during the year?
c. What number of annual flying hours was exceeded by only 15% of the aircraft?
d. What number of annual flying hours was exceeded by 75% of the aircraft?