You want to invest an amount of money today and receive back twice that amount in the future. You expect to earn 9 percent interest. Approximately how long must you wait for your investment to double in value?

The answer is 8 years

Explanation:

FV = PV (1+r) ^n

Where

PV = let's assume PV is $100

FV = Since FV will be doubled, the we have $200 ($100 x 2)

n=?

r = 9percent

Let us use the rule of 72 which states that an investment will double when:

Annual Investment Rate x Number of Years = 72.

Number of years = 72/9

= 8 years

The investment is doubled in 8 years at the rate of 9percent