Are people moving away from having a traditional land line t

Are people moving away from having a traditional land line telephone in their homes? A random sample of 153 people was asked \'\'Do you have a traditional telephone in your place of residence?\'\' Of those asked, 95 said they do have a traditional telephone. The 99% confidence interval estimate is: Select one: a. (0.544, 0.698) b. (0.278, 0.480) c. (0.617, 0.625) d. (0.520, 0.722)

Solution

Confidence Interval For Proportion
CI = p ± Z a/2 Sqrt(p*(1-p)/n)))
x = Mean
n = Sample Size
a = 1 - (Confidence Level/100)
Za/2 = Z-table value
CI = Confidence Interval
Mean(x)=95
Sample Size(n)=153
Sample proportion = x/n =0.621
Confidence Interval = [ 0.621 ±Z a/2 ( Sqrt ( 0.621*0.379) /153)]
= [ 0.621 - 2.58* Sqrt(0.002) , 0.621 + 2.58* Sqrt(0.002) ]
= [ 0.52,0.722]