Answer:
a) 7 years for the investment to double in value.
b) 10 years for the investment to double in value.
Step-by-step explanation:
The rule of 70% states that, for an investment to double in value, the required time is 70/r, in which r is the annual interest rate, as a percent.
So
(a) r = 10%
It is going to take 70/10 = 7 years for the investment to double in value.
(b) r = 7%
It is going to take 70/7 = 10 years for the investment to double in value.
