The Post Office has established a record in a major midwestern city for delivering 90 percent of its local mail the next working day. When there are 8 local letters mailed, what is the probability that the number delivered will be within 2 standard deviations of the mean?
A) .9950
B) .9619
C) .8131
D) .9996

Question

Quizplus · Accepted Answer

P[σ = 7.2 ± 2(.85)] = P(σ = 7.2 ± 1.7) = P(5.5 ≤ x ≤8) = P(6 ≤ x ≤8)
= .4305 + .3826 + .1488 = .9619

The Post Office Has Established a Record in a Major