A 6 litre sol is 20% alcohol .How many litres of pure alcohol must be added to produce a sol that is 50% alcohol ?	Choose one:
A) a . 0.6 B) b . 1 C) c . 2.1 D) d . 3.6 E) e . 5.4

Rationale: "20 % of 6 = 1.2 50 % of 6 = 3 shortage is 1.8 so we need to have 1.8 / 50 % to get 50 % alcohol content . = 3.6 d"
Answer: D