# More Examples of Compound Interest

To Find Principal
We are given n, A, and r
We have to find P by the formula
${\text{A}} = {\text{P}}{\left( {1 + {\text{r}}} \right)^n} \Rightarrow {\text{P}} = \frac{{\text{A}}}{{{{\left( {1 + {\text{r}}} \right)}^n}}}$
Example 01:
Find principal, when compound interest for 4 years at 6% is 525.
Solution:
Let Principal = P, $n = 4$, r = 6%, C.I = 525
We know that

To Find Rate
When P, n, A are given

We have to find r by the using same formula
${\text{A}} = {\text{P}}{\left( {1 + {\text{r}}} \right)^n}$

Example 02:
Find the rate of interest compounded per annum for 3 years so that 4000 becomes 4635.50
Solution:
Let A = 4635.50, P = 4000, $n = 3$, r = ?
Using ${\text{A}} = {\text{P}}{\left( {1 + {\text{r}}} \right)^n}$