Determining Sample Size. In Exercises 31-38, use the given data to find the minimum sample size required to estimate a population proportion or percentage. find the sample ded to estima sidents who are and 6 adie in parts (2(6) change if the entire United S stead of C 32. Chickenpox You plan to conduct a survey to estimate the percentage of adults who have had chickenpox. Find the number of people who must be surveyed if you want to be 90% con- fident that the sample percentage is within two percentage points of the true percentage for the population of all adults. a. Assume that nothing is known about the prevalence of chickenpox. b. Assume that about 95% of adults have had chickenpox. c. Does the added knowledge in part (b) have much of an effect on the sample size