statistics
posted by Arlene on .
The general manager for Gordon's Self Service Gasoline is interested in estimating the mean number of gallons of gasoline that are purchased by customers at their Philadelphia location. He would like his estimate to be within plus or minus 0.50 gallons, and he would like the estimate to be at a 99% confidence level. Past studies have shown that the standard deviation for purchase amount is 4.0 gallons. Find the required sample size.

Formula:
n = [(zvalue * sd)/E]^2
...where n = sample size, zvalue will be 2.58 using a ztable to represent the 99% confidence interval, sd = 4, E = 0.5, ^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.