Walking into a Walmart store at $2$:$00$ a$.$m$.$ with a friend to buy some cat food, your friend says, $$I can$$t believe that these stores stay open all night. There are $10$ shoppers in this store, and only one checkout lane is open. It doesn$$t make any sense for this store to be open all night.$$ Why do you think this Walmart is open all night? Are the costs of rent, equipment, fixtures, salaries of management, and so on rel$$evant when Walmart makes the decision whether to stay open all night?