6.50 Sample size determination. Refer to Example 6.3 (page 293) to find the standard deviation of the delay departures for Delta Airlines is given by 25.83. (a) Use the sample size formula (page 311) to determine what sample size you need to have a margin of eror equal to two minutes with 90% confidence. Explain why you must always round up to the next higher whole number when using the formula for n. (b) What sample size do you need to have a margin of error equal to two minutes with 95% confidence