A nurse at a local hospital is interested in estimating the birth weight of infants. How large a sample must she select if she desires to be 95% confident that the true mean is within 3 ounces of the sample mean? The
Standard deviation of the birth weights is known to be 6 ounces.
A)16
B)15
C)4
D)3

Question

Quizplus · Accepted Answer

The sample size needed can be calculated using the formula for the sample size in estimating a mean, n = (Z*σ/E)^2, where Z is the Z-value for the desired confidence level (1.96 for 95% confidence), σ is the population standard deviation (6 ounces), and E is the margin of error (3 ounces). Plugging in the values gives n = (1.96*6/3)^2 = 15.36, which rounds up to 16 to ensure the sample is large enough.

A Nurse at a Local Hospital Is Interested in Estimating