Question

The simple interest on a certain sum for $8$ months at $4\%$ simple interest is $Rs.129$ less than the simple interest on the same sum for $15$ months at $5\%$ per annum. Then the sum is

• A. $Rs.3,400$
• B. $Rs.3,500$
• C. $Rs.3,600$
• D. $Rs.3,700$

Answer 1

The correct option is C $Rs.3,600$

Let the sum be $x$.

According to the question,

$\begin{array}{cc}\frac{x\times 8\times 4}{12\times 100}& =\frac{x\times 15\times 5}{12\times 100}-129\\ \frac{x\times 15\times 5}{12\times 100}-\frac{x\times 8\times 4}{12\times 100}& =129\\ \frac{75x-32x}{12\times 100}& =129\\ \frac{43x}{12\times 100}& =129\\ x& =Rs.3600\end{array}$

Hence, option $C$ is correct.