1-gallon can to within 10.004 gallon the standard deviation is 0.02 gallon, what sample size is needed? 8.40 If a quality control manager wants to estimate, with 95% confidence, the mean life of light bulbs to within +20 hours and also assumes that the population standard deviation is 100 hours, how many light bulbs need to be selected? 8.41 If the inspection division of a county weights and measures department wants to estimate the mean amount of soft-drink fill in 2-liter bottles to within 10.01 liter with