In some quantity of ghee, 60\% is pure ghee and 40\% is vanaspati. If 10 kg of pure ghee is added, then the strength of vanaspati ghee becomes 20\%. The original quantity was
(a)10 kg
(b)15 kg
(c)20 kg
(d)25 kg
Answer
Answer (as printed): A
Explanation
Let the original quantity be $x \mathrm{kg}$. Vanaspati ghee in $x \mathrm{kg}$ $$\begin{aligned} & =\left(\frac{40}{100} x\right) \mathrm{kg}=\left(\frac{2 x}{5}\right) \mathrm{kg} . \\ & \text { Now, } \frac{\frac{2 x}{5}}{x+10}=\frac{20}{100} \Leftrightarrow \frac{2 x}{5 x+50}=\frac{1}{5} \Leftrightarrow 5 x=50 \Leftrightarrow x=10 . \end{aligned}$$