Some of 60%-intensity red paint is replaced with 30% solution of red paint such that the new paint intensity is 40%. What fraction of the original paint was replaced?
Choose the correct option:
A) 2 / 3
B) 1 / 3
C) 2 / 5
D) 1 / 2
E) 1 / 5

Rationale: "let total paint = 1 let amount replaced = x 60 ( 1 - x ) + 30 x = 40 x = 2 / 3 answer : a"
Answer: A