In an intra-squad swim competition, men's freestyle 100 swim times at a certain university ranged from 43.89 seconds to 51.96 seconds. (a) Estimate the standard deviation using Method 3 (the Empirical Rule for a normal distribution). (Round your answer to 3 decimal places.) Standard deviation (b) What sample size is needed to estimate the mean for all swimmers with 95 percent confidence and an error of ±0.50 second? (Enter your answer as a whole number (no decimals). Use a z-value taken to three decimal places in your calculations.) Sample size