Carla Has Decided to Purchase a $30,000 Car

Short Answer

Carla has decided to purchase a $30,000 car. She can either liquidate some of her investments and pay cash, or accept the dealer's terms of $7000 down and successive payments of $10,000, $9000, and $8000 at the end of each of the next three years.
a) Which choice should Carla make if she can earn 7% compounded semiannually on her investments? In current dollars, how much is the economic advantage of the preferred alternative?
b) Which choice should Carla make if she can earn 10% compounded semiannually on her investments? In current dollars, how much is the economic advantage of the preferred alternative?