A sum of money, when invested at 10% compound interest per annum, amounts to ₹1,815 after 2 years. What is the original sum that was invested in the beginning?

Correct option is D

Given:

Amount after 2 years = ₹1,815

Rate of compound interest = 10% per annum

Time = 2 years

Formula Used:

P =$$\frac{A}{\left(1 + \frac{R}{100} \right)^T}$$​

Where A is amount, P is principal, R is rate, and T is time.

Solution:

P =$$\frac{1815}{\left(1 + \frac{10}{100} \right)^2} = \frac{1815}{(1.1)^2} = \frac{1815}{1.21} = 1500$$

Alternate Method:

Rate of compound interest = 10% =$$\frac {1}{10}$$

1st year   10   :   11

2nd year   10 :    11 
                100 :   121

Principal = $$\frac {1815}{121}\times 100$$ = 1500​

The original sum invested was ₹1,500.