In the Ardmore Hotel, 28 percent of the guests (the historical percentage) pay by American Express credit card. (a) What is the expected number of guests until the next one pays by American Express credit card? (Round your answer to 2 decimal places.) Expected number of guests (b) What is the probability that the first guest to use an American Express is within the first 13 to checkout? (Round your answer to 4 decimal places.)