A certain sum amounts to ₹20720 in four years and ₹24080 in six years at a certain rate of simple interest. The sum (in ₹) is:

A certain sum amounts to ₹20720 in four years and ₹24080 in six years at a certain rate of simple interest.

$$20720=P+\frac{P\times\ R\times\ 4}{100}$$

$$20720=P+0.04PR$$    Eq.(i)

$$24080=P+\frac{P\times\ R\times\ 6}{100}$$

$$24080=P+0.06PR$$    Eq.(ii)

$$\frac{Eq.(i)}{Eq.(ii)}  = \frac{P+0.04PR}{P+0.06PR} =  \frac{20720}{24080}$$

$$\frac{1+0.04R}{1+0.06R}=\frac{37}{43}$$

43+1.72R = 37+2.22R

43-37 = 2.22R-1.72R

0.5R = 6

R = 12

Put the value of R in Eq.(i).

$$20720=P+0.04P\times12$$

20720=P+0.48P

1.48P = 20720

P = 14000