The difference between simple and compound interests compounded annually on a certain sum of money for 2 years at 9% per annum is Rs 405. The sum is ____.

The formula for the difference (D) between compound interest (CI) and simple interest (SI) for a period of 2 years is given by:
D=P(
100
R
​
)
2

Where:

D=Difference=Rs 405

R=Rate of interest=9% per annum

P=Principal sum

Substituting the given values into the formula:

405=P(
100
9
​
)
2

405=P×
10000
81
​

P=
81
405×10000
​

Since
81
405
​
=5:

P=5×10000=Rs 50000