Elwin Osbourne, CIO at GFS, Inc., is studying employee use of GFS e-mail for non-business communications.He plans to use a 95% confidence interval estimate of the proportion of e-mail messages that are non-business; he will accept a 0.05 error.Previous studies indicate that approximately 30% of employee e-mail is not business related.Elwin should sample _______ e-mail messages.
A)323
B)12
C)457
D)14
E)100

Question

Quizplus · Accepted Answer

To calculate the sample size needed for a proportion, the formula is $n = \frac{Z^2 \times p(1-p)}{E^2}$, where $Z$ is the Z-value for the desired confidence level (1.96 for 95%), $p$ is the estimated proportion (0.30), and $E$ is the margin of error (0.05). Plugging in the values: $n = \frac{1.96^2 \times 0.30(1-0.30)}{0.05^2} \approx 323$.