Americans are increasingly skimping on their sleep (National Geographic News, February 24, 2005). A health expert believes that American adults sleep an average of 6.2 hours on weekdays with a standard deviation of 1.2 hours. To answer the following questions, assume that sleep time on weekdays is normally distributed.

a. What percentage of American adults sleep more than 8 hours on weekdays?

b. What percentage of American adults sleep less than 6 hours on weekdays?

c. What percentage of American adults sleep between 6 and 8 hours on weekdays?