The center for disease control and prevention (cdc) estimates that, on average, 5% to 20% of the u. s. population gets the flu each year. using 20% as our best guess (p∗), find how large a sample would be needed to get a ± 2 percentage point margin of error on a 95% confidence interval for the population proportion of americans who get the flu in a given year. (enter your answer as whole number.)