answer for my question

Question

A researcher studying the lifespan of a certain species of bacteria. A preliminary sample of 25 bacteria reveals a sample mean of  hours with a standard deviation of  hours. He would like to estimate the mean lifespan for this species of bacteria to within a margin of error of 0.5 hours at a 99% level of confidence.What sample size should you gather to achieve a 0.5 hour margin of error?

Answer 1

sample size (n) = (z for 99.5 probability * s / ME)^2