If you invest $5000 at 4% compounded semiannually, how long will it take for your investment to grow to $8,000. (in complete years)

If an amount P is invested for n terms at a rate of interest of
r, it grows to P*(1 + r)^n.

Here, the annual rate of interest is 4%,
as the compounding is done semi-annually, the effective rate for a term is 4/2 =
2%.

Let the number of terms be n.

We
have to solve 8000 = 5000*(1 + 0.02)^n

=> 8/5 =
1.02^n

take the log of both the
sides

=> n = log(8/5) / log
(1.02)

=> n = 23.73

The term n
is in half years, 23.73 terms rounded to the nearest year gives 12
years.

The time taken for the investment to grow to
$8000 is 12 years.