If the annual rate of simple interest increases from $10 \%$ to $12 \frac{1}{2} \%$, a man's yearly income increases by ₹ 1250. His principal (in ₹) is
(a)₹ 45,000
(b)₹ 50,000
(c)₹ 60,000
(d)₹ 65,000
Answer
Answer (as printed): B
Explanation
Let the sum be ₹ $x$. Then, $\left(x \times \frac{25}{2} \times \frac{1}{100}\right)-\left(\frac{x \times 10 \times 1}{100}\right)=1250$ $$\Leftrightarrow \quad 25 x-20 x=250000 \Leftrightarrow 5 x=250000 \Leftrightarrow x=50000 \text {. }$$
Explanation as extracted from the printed page; notation may be imperfect.