posted by Valerie .
A researcher is interested in estimating the noise levels in decibels at area urban hospitals. She wants to be 90% confident that her estimate is correct. If the standard deviation is 4.13, how large a sample is needed to get the desired information to be accurate within 0.68 decibels?
n = [(z-value * sd)/E]^2
...where n = sample size, z-value will be found using a z-table for 90% confidence, sd = 4.13, E = 0.68, ^2 means squared, and * means to multiply.
Plug the values into the formula and finish the calculation. Round your answer to the next highest whole number.