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  Vanaspathi ghee become 20%. The original quantity was:

Solution: Let intial quantity of  ghee = 100x

it contains $60\%$ pure ghee = 60x and 40x  vanaspati

total weight (100x +10) kg it contains = (60x + 10) kg pure ghee and 40x vanaspati

$\begin{array}{l}\frac{40x}{100x+10}=\frac{20}{100}\\ \Rightarrow 200x=100x+10\\ \Rightarrow 100x=10\text{\hspace{0.17em}\hspace{0.17em}}whichis\text{\hspace{0.17em}\hspace{0.17em}intial\hspace{0.17em}}weightofghee\end{array}$