A large national company is considering negotiating cellular phone rates for its employees. The Human Resource department would like to estimate the proportion of its employee population who own an Apple iPhone. A random sample of size 250 is taken and 40% of the sample own an iPhone. The 90% confidence interval to estimate the population proportion is ___.
A) 0.35 to 0.45
B) 0.34 to 0.46
C) 0.37 to 0.43
D) 0.39 to 0.41
E) 0.40 to 0.45

Question

Quizplus · Accepted Answer

The margin of error for a 90% confidence interval is 1.645 * sqrt((p(1-p))/n) = 1.645 * sqrt((0.4(1-0.4))/250) = 0.05. So the confidence interval is 0.4 +/- 0.05, or 0.35 to 0.45.

A Large National Company Is Considering Negotiating Cellular Phone Rates