Question

How long does it take $6,000 to quadruple if it is invested at 9.1% interest compounded annually?

a
15.9 years
b
17.8 years
c
37 years
d
222,222.22 years

Answer 1

1. 15.9 years

Explanation:

You must solve this equation:

`6000 \cdot 1.091^n > 24000`

So
`1.091^n > 4`

Take the log left and right:

`\log 1.091^n > \log 4`

use the log property that you can put the exponent in front:

`n \cdot \log 1.091 > \log 4`

`n > (\log 4)/(\log 1.091)`

n > 15.917