In some quantity of ghee, 50% is pure ghee and 50% is vanaspati. If 20kg of pure ghee is added, then the strength of vanaspati ghee becomes 30%. The original quantity was? Pick one: A) 25 B) 15 C) 30 D) 45 E) 20

Rationale: "let the original quantity be x then , vanaspati ghee in xkg = 50 x / 100 kg = x / 2 kg ( x / 2 ) / ( x + 20 ) = 30 / 100 x / ( 2 x + 40 ) = 3 / 10 x = 30 answer is c"
Answer: C