1. **State the problem:** Ramani deposited an amount $P$ for two years at an annual compound interest rate of 10%. The interest earned in the second year is 660 and the total amount after two years is 7260. We need to find the principal amount $P$.
2. **Formula for compound interest:** The amount after $n$ years with interest rate $r$ compounded annually is given by:
$$ A = P(1 + r)^n $$
where $A$ is the amount, $P$ is the principal, $r$ is the rate in decimal, and $n$ is the number of years.
3. **Calculate the amount after the first year:**
$$ A_1 = P(1 + 0.10) = 1.1P $$
4. **Calculate the amount after the second year:**
$$ A_2 = A_1(1 + 0.10) = 1.1 imes 1.1P = 1.21P $$
5. **Given total amount after two years:**
$$ A_2 = 7260 $$
So,
$$ 1.21P = 7260 $$
6. **Calculate principal $P$ from total amount:**
$$ P = \frac{7260}{1.21} $$
$$ P = \frac{7260}{\cancel{1.21}} \times \cancel{\frac{1}{1.21}} = 6000 $$
7. **Calculate interest for the second year:**
Interest for second year = Amount at end of second year - Amount at end of first year
$$ = 1.21P - 1.1P = 0.11P $$
Given this interest is 660,
$$ 0.11P = 660 $$
8. **Calculate principal $P$ from second year interest:**
$$ P = \frac{660}{0.11} = 6000 $$
9. **Conclusion:** Both methods confirm the principal amount deposited is **6000**.
Compound Interest 599C19
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