A certain amount money at R% compounded annually after two and three years becomes Rs. 1440 and Rs. 1728 respectively, R% is ?

Answer: Option D

Here, b – a = 3 – 2 = 1
B = Rs. 1728, A = Rs.1440
$$\begin{array}{rl}& R\%=\left(\frac{B}{A}-1\times 100\right)\%\\ & =\left(\frac{1728}{1440}-1\times 100\right)\%\\ & =\left(\frac{288}{1440}\times 100\right)\%\\ & =20\%\end{array}$$