10-15. The following items pertain to determining sample size when a mean is involved. Calculate the samble size for each case. 10-10. Last year, Lipton Tea Company conducted a mall-intercept study at six regional malls around the country and found that 20% of the public preferred K-cup (Keurig) tea over bagged or bottled tea. This year, Lipton wants to have a nationwide telephone survey performed with random digit dialing. What sample size should be used in this year's study to achieve an accuracy level of 2.5% at the 99% level of confidence? What about at the 95\% level of confidence? 10-5. Using the formula provided in your text, determine the approximate sample sizes for each of the following cases, all with precision (allowable error) of 5% : a. Variability of 30%, confidence level of 95% b. Variability of 60%, confidence level of 99% c. Unknown variability, confidence level of 95%