₹3600 becomes ₹4900 in 2 years when kept at compound interest (compounded annually). What is the rate of interest per annum?

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

Where A = principal amount + interest

P = principal amount

R = rate of interest

T = time

$$4900=3600\left(1+\frac{R}{100}\right)^2$$

$$\frac{4900}{3600}=\left(1+\frac{R}{100}\right)^2$$

$$\frac{49}{36}=\left(1+\frac{R}{100}\right)^2$$

$$\left(\frac{7}{6}\right)^2=\left(1+\frac{R}{100}\right)^2$$

$$\frac{7}{6}=1+\frac{R}{100}$$

$$\frac{7}{6}-1=\frac{R}{100}$$

$$\frac{1}{6}=\frac{R}{100}$$

$$\frac{100}{6}=R$$

$$\frac{50}{3}=R$$

$$R\ =\ 16\frac{2}{3}$$%