suppose that cathy spends all of her income on 20 units of good x and 25 units of good y. cathy's marginal utility from the 20th unit of good x is 9 utils, and her marginal utility from the 25th unit of good y is 17 utils. if the price of good x is $0.50 per unit and the price of good y is $1.00 per unit, then to comply with the rational spending rule, cathy should:

(a) purchase more than 20 units of good x and less than 25 units of y.
(b) purchase less than 20 units of good x and more than 25 units of good y.
(c) purchase more than 20 units of good x and more than 25 units of good y.
(d) continue to purchase 20 units of good x and 25 units of good y.

Suppose that a major city’s main thoroughfare, which is also an interstate highway, will be completely closed to traffic for two years, from january 2014 to december 2015, for reconstruction at a cost of $535 million. if the construction company were to keep the highway open for traffic during construction, the highway reconstruction project would take much longer and be more expensive. suppose that construction would take four years if the highway were kept open, at a total cost of $800 million. the state department of transportation had to make its decision in 2014, one year before the start of construction (so that the first payment was one year away). so the department of transportation had the following choices: (i) close the highway during construction, at an annual cost of $267.5 million per year for two years. (ii) keep the highway open during construction, at an annual cost of $200 million per year for four years. now suppose the interest rate is 80%. calculate the present value of the costs incurred under each plan.