2. An experiment is required to estimate the standard deviation of a process to within ±20% of its true value with 95% confidence, i.e. a confidence interval for the population standard deviation of the following form is required: P(s(1 − 8) < σ < s(1+8)) = 0.95 where s will be determined from the sample data. Calculate the sample size for the experiment assuming that the distribution is normal.