To the closest year, how long will it take $200 to double if it is deposited and earns the following rates? [Notes: (1) See the hint for Problem 2-1. (2) This problem cannot be solved exactly with some financial calculators. For example, if you enter PV _ _200, PMT _ 0, FV _ 400, and I _ 7 in an HP-12C, and then press the N key, you will get 11 years for part a. The correct answer is 10.2448 years, which rounds to 10, but the calculator rounds up. However, the HP-10B gives the correct answer.]
a. 7 percent.
b. 10 percent.
c. 18 percent.
d. 100 percent.