Question

A sum of money becomes Rs. 13,380 after 3 years and Rs. 26,760 after 6 years on compound interest. The sum is :

• A. 6680
• B. 6290
• C. 9060
• D. 6690

Answer 1

Answer:

D. 6690

The sum of money is Rs. 6,690.

In compound interest, the amount increases by the same factor over equal intervals of time.

1. Set up the formulas:
   Let the principal sum be $P$ and the growth factor for 3 years be $X$.

   • Amount after 3 years: $P \times X = 13,380$ --- (Equation 1)

   • Amount after 6 years: $P \times X^2 = 26,760$ --- (Equation 2)

2. Find the growth factor ($X$):
   Divide Equation 2 by Equation 1:
   $X = \frac{26,760}{13,380} = 2$ (This means the money exactly doubles every 3 years).

3. Calculate the Principal ($P$):
   Substitute the value of $X = 2$ back into Equation 1:
   $P \times 2 = 13,380$

   $P = \frac{13,380}{2} = \mathbf{6,690}$