Some of 50%-intensity red paint is replaced with 25% solution of red paint such that the new paint intensity is 35%. What fraction of the original paint was replaced?
Choose the correct choice from the following:
A) 1 / 35
B) 1 / 5
C) 2 / 3
D) 3 / 5
E) 4 / 5

Rationale: "35 % is 10 % - points above 25 % and 15 % - points below 50 % . thus the ratio of 25 % - solution to 50 % - solution is 3 : 2 . 3 / 5 of the original paint was replaced . the answer is d ."
Answer: D