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
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 3/5.
<result>D</result>
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?