Find probability

Question

Suppose that about 85% of graduating students attend their graduation. A group of 22 graduating students is randomly chosen.

Find the probability that 19 or 20 attend. (Round your answer to four decimal places.)

Answer 1

mean = np = 22(.85) = 18.7

variance = npq = 18.7(1-.85) = 18.7(.15) = 2.805

standard deviation = sqrnpq = sqr2.805 = 1.674813422

z score = (20-18.7)/1.6748134 = 1.3/1.6748134 = .7762058642

and (19-18.7)/1.6748134 = .3/1.6748134= .5024440268

use z tables or calculator to find Pr(19 or 20)=.088864 = 8.8864%