A sum invested at 5\% simple interest per annum grows to ₹ 504 in 4 years. The same amount at 10\% simple interest per annum in $2 \frac{1}{2}$ years will grow to :
(a)₹ 420
(b)₹ 450
(c)₹ 525
(d)₹ 550
Answer
Answer (as printed): C
Explanation
Let the sum be ₹ $x$. Then, S.I. $=₹(504-x)$. $\therefore \quad\left(\frac{x \times 5 \times 4}{100}\right)=504-x \Leftrightarrow 20 x=50400-100 x$ $\Leftrightarrow 120 x=50400 \Leftrightarrow x=420$. Now, $P=₹ 420, R=10 \%, T=\frac{5}{2}$ years. S.I. $=₹\left(\frac{420 \times 10}{100} \times \frac{5}{2}\right)=₹ 105$. $\therefore$ Amount $=₹(420+105)=₹ 525$.
Explanation as extracted from the printed page; notation may be imperfect.