Background data: "Only 25% of people prefer my pizza!?" Clark exclaims in disbelief. Livid once again, he vows to fight Lex with data. He hatches a plan to assemble his own focus group for a blind taste test.

Question: What is the minimum number of randomly selected people Clark should include in his focus group if he wants to be sure that he will be able to calculate a 95% confidence interval no larger than "plus or minus 0.05" for the true proportion of people who prefer Clark's pizza?

Please answer the question using excel functions. Please show excel formulas and calculations used in getting the answer.