The cafeteria at Acme Company can offer only four main dishes at lunchtime, and the same four choices have been offered for years  Recently mushroom casserole was offered in place of one of the other main dishes for two days, during which more people chose mushroom casserole than any other main dish
Clearly, if the cafeteria wants to please its customers, mushroom casserole should replace one of the regular dishes as a permanent part of the menu
the proportion of Acme Company employees who regularly eat lunch in the company cafeteria