It is known that approximately 20% of the population is colour blind. In a sample of 270 people, use the normal approximation to find probability that:

Question

a)at least 90 people are colour blind
b)exactly 50 people are colour blind
Thanks

Answer 1

mean=54
variance=.2(1-.2)270=.16*270=43.2
standard deviation:sqrt(43.2)=6.8

does that help?

Answer 2

Thanks.
My solution is:
n=270
p=0.2
np=54
np(1-p)=43.2
sqrt(np(1-p))=sgrt43.2=6.57
z=90-54/6.57=5.479
I don't know how to find the probability that at least 90 people are colour blind, and probability that exactly 50 people are colour blind.
P[x>90]
P[x=50]
Thanks.