A certain quantity of 60% solution is replaced with 25% solution such that the new concentration is 35%. What is the fraction of the solution that was replaced?
Answers.
A) 1 / 4	B) 1 / 3	C) 1 / 2	D) 2 / 3	E) 5 / 7

Rationale: "let ' s say that the total original mixture a is 100 ml the original mixture a thus has 60 ml of alcohol out of 100 ml of solution you want to replace some of that original mixture a with another mixture b that contains 25 ml of alcohol per 100 ml . thus , the difference between 60 ml and 25 ml is 35 ml per 100 ml of mixture . this means that every time you replace 100 ml of the original mixture a by 100 ml of mixture b , the original alcohol concentration will decrease by 35 % . the question says that the new mixture , let ' s call it c , must be 35 % alcohol , a decrease of only 25 % . therefore , 25 out of 35 is 5 / 7 and e is the answer ."
Answer: E