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

18.7 = expected number, = mean= np = 22 x .85

q= .15

variance = npq = 18.7x.15 = 2.805

sd= sqr(var)=1.6748

binomial distribution

z scores = (19-18.7)/1.6748= .3/1.6749=.1791

and (20-18.7)/1.6748 = 1.3/1.6748= .7762

use z tables or calculator to find the area = pr(19 or 20)=.21011= 21.011% chance 19 or 20 show up