If the exchange rate is 2 Brazilian reals per dollar and a meal in Rio costs 20 reals, then how many dollars does it take to buy a meal in Rio?

A firm will choose to minimize their costs subject to their ______________

Fill in the blank(s) with the appropriate word(s).

Which of the following about costs is always true?

a. When marginal costs are less than average total costs, average total costs will be decreasing. b. When average fixed costs are falling, marginal costs must be less than average fixed costs. c. When average fixed costs are rising, marginal costs must be greater than average total costs. d. When marginal costs are greater than average total costs, average total costs will be decreasing.