Question

Construct a confidence interval of the population proportion at the given level of confidence. x = 120, n = 1200, 95% confidence Click here to view the standard normal distribution table (page 1). Click here to view the standard normal distribution table (page 2). The lower bound of the confidence interval is LI. (Round to three decimal places as needed.)
and i need help finding the upper bound confidence interval as well

Answer 1

Solution :

Given that x = 120, n = 1200

=> p = x/n

= 120/1200

= 0.1

=> q = 1 - p = 0.9

=> For 95% confidence level, Z = 1.96

=> The lower bound of the confidence interval is

=> p - Z*sqrt(p*q/n)

=> 0.1 - 1.96*sqrt(0.1*0.9/120)

=> 0.0463

=> 0.046 (rounded)

=> The upper bound of the confidence interval is

=> p + Z*sqrt(p*q/n)

=> 0.1 + 1.96*sqrt(0.1*0.9/120)

=> 0.1537

=> 0.154 (rounded)