A marketing research firm conducted a survey to determine how adults in Philadelphia use their cell phones. The survey randomly sampled 250 adults. One question asked in the survey was “Over the past month have you used your cell phone to pay a credit card bill?” The sampled responses to this question are contained in the file CellPhone.
a. How many of the 250 randomly sampled adults in Philadelphia used their cell phone last month to pay a credit card bill?
b. What point estimate should the marketing research firm use to estimate the true population proportion of adults in Philadelphia who used their cell phones last month to pay a credit card bill?
c. Construct a 95% confidence interval estimate for the true proportion of adults in Philadelphia who used their cell phones last month to pay a credit card bill.

d. For a 90% confidence interval estimate of the true proportion of adults who used their cell phone last month to pay a credit card bill, what sample size is required if the marketing research firm wants a margin of error that is no higher than ±0.02?