A sum of money amounted to ₹ 720 in 2 years and ₹ 792 in 3 years when interest is compounded annually. The annual rate of interest, (in %) is:

Let the Principal be Rs.P and Rate of interest be R%
Given, $$P(1+\dfrac{R}{100})^3 = 792$$ and $$P(1+\dfrac{R}{100})^2 = 720$$
Dividing first equation by second equation.
$$\dfrac{P(1+\dfrac{R}{100})^3}{P(1+\dfrac{R}{100})^2} = \dfrac{792}{720}$$

=> $$1+\dfrac{R}{100} = \dfrac{792}{720}$$

=> $$\dfrac{R}{100} = \dfrac{792}{720} - 1$$

=> $$\dfrac{R}{100} = \dfrac{72}{720} = \dfrac{1}{10}$$
Therefore, R = 10%