A chemical supply company has 60 liters of a 35% HNO3 solution. How many liters of pure undiluted HNO3 must the chemists add so that the resultant solution is a 50% solution? Pick:
A) 18
B) 15
C) 20
D) 24
E) 30

Rationale: "60 liters of a 35 % hno 3 solution means hno 3 = 21 liters in 60 liters of the solution . now , let x be the pure hno 3 added . as per question , 21 + x = 50 % of ( 60 + x ) or x = 18 hence , a"
Answer: A