According to the National Restaurant Association, hamburgers are the number-one-selling fast-food item in the United States. An economist studying the fast-food-buying habits of Americans paid graduate students to stand outside two suburban McDonald's restaurants near Boston and ask departing customers whether they spent more or less than $2.25 on hamburger products for their lunch. Twenty answered "less than"; 50 said "more than"; and 10 refused to answer the question.

a. Is there sufficient evidence to conclude that the median amount spent for hamburgers at lunch at McDonald's is less than $2.25?

b. Does your conclusion apply to all Americans who eat lunch at McDonald's? Justify your answer.

c. What assumptions must hold to ensure the validity of your test in part a?