The Simple Interest on a certain sum at the rate of 5% per annum for 3 years is Rs.1260. Find the Compound Interest for that sum at the same rate and for the same period.

Given data in the question is clearly,  Rate=5%

                                                                 Time=3years

                                                                  Simple interest=1260₹

Formula is Simple interest=$$\frac{principal×rate of interest×time}{100}$$

So we can write as,  principal=$$\frac{simple interest×100}{rate of interest×time}$$

                                                    =$$\frac{1260×100}{5×3}$$

                                    Principal =8400₹

Before finding compound interest we need to find amount

Formula for amount is 

Amount=principal×(1+$$\frac{rate}{100})^n$$

              =8400×(1+$$\frac{5}{100})^3$$

              =8400×($$\frac{105}{100})^3$$

              =8400×($$\frac{21}{20})^3$$

By solving we get Amount=9724.05₹

To calculate compound interest formula is C.I=A-P

That is compound interest=Amount-principal 

                                               =₹(9724.05-8400)

             Compound interest=1324.05₹