Vishwas borrowed a total amount of Rs. 30000, part of it on simple interest rate of 12 p.c.p.a. and remaining on simple interest rate of 10 p.c.p.a. If at the end of 2 year she paid in all Rs. 36480 to settle the loan amount, what was the amount borrowed at 12 p.c.p.a ?

A. Rs. 12000 B. Rs. 16000 C. Rs. 17500 D. Rs. 18000 Answer: Option A
Let the sum borrowed at 12% p.a. be Rs. x and that borrowed at 10% p.a. be Rs. (30000 – x) S.I. at the end of 2 years = Rs. (36480 – 30000) = Rs. 6480 $\begin{array}{l}\therefore\left(\frac{x\times12\times2}{100}\right)+\left[\frac{(30000-x)\times10\times2}{100}\right]=6480\\ \Leftrightarrow24x+600000-20x=648000\\ \Leftrightarrow4x=48000\\ \Leftrightarrow x=12000\end{array}$