Question

Thirty percent of a magazine's subscribers are female. A random sample of 50 subscribers is taken. Answer the following questions using Excel.

a.	What is the probability that the proportion of females from this sample is at most 0.25?
b.	What is the probability that the proportion of females from this sample is between 0.22 and 0.28?
c.	What is the probability that the proportion of females from this sample is within .03 of the population proportion?

Answer 1

excel formulae are in bold:

std error of proportion=σp=√(p*(1-p)/n)=0.0648

a)

probability that the proportion of females from this sample is at most 0.25:

=norm.dist(0.25,0.3,0.0648,true)=0.2202

b)

probability that the proportion of females from this sample is between 0.22 and 0.28:

=norm.dist(0.28,0.3,0.0648,true)-norm.dist(0.22,0.3,0.0648,true)=0.2703

c)

probability that the proportion of females from this sample is within .03 of the population proportion:

=norm.dist(0.33,0.3,0.0648,true)-norm.dist(0.27,0.3,0.0648,true)=0.3566