A survey of U.S. adults ages 18-29 found that 93% use the Internet. You randomly

Question

A survey of U.S. adults ages 18-29 found that 93% use the Internet. You randomly select 100 adults ages 18-29 and ask them if they use the Internet. If you can, use the normal distribution to approximate the indicated probabilities and sketch their graphs. Find the probability that exactly 90 people say they use the Internet. Find the probability that at least 90 people say they use the Internet. Find the probability that fewer than 90 people say they use the Internet. Are any of the probabilities in parts(a) - (c) unusual? Explain.

Explanation / Answer

here p=0.93 ; n=100

mean =np=93

std deviation=2.55147

z score =(X-mean)/std deviation

a)P(X=90)=P(89.5<X<90.5)=P(-1.3716<Z<-0.9798)=0.1636-0.0851=0.0785

b)P(X>=90)=1-P(X<89.5)=1-P(Z<-1.3716)=1-0.0851=0.9149

c)P(X<90)=1-P(X>=90)=1-0.9149=0.0851

d)No; as all probabilities lie b/w 0.05 and 0.95 ; hence none of them are unusual

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