The post office has established a record in a major midwestern city for delivering 90 percent of its local mail the next working day. answer the following questions based on this information:

a. if you mail eight local letters, what is the probability that all of them will be delivered the next day?
b. if you mail eight local letters, what is the average number you expect to be delivered the next day?
c. calculate the standard deviation of the number delivered when 8 local letters are mailed.
d. when there are 8 local letters mailed, what is the probability that the number delivered will be within 2 standard deviations of the mean?