This concept has yet to make sense to me (alligation i think its called), but it yields the correct answer. Can someone offer up a Barney-style explanation of this concept?
From "Tough Gmat math problems"
7. A certain quantity of 40% solution is replaced with 25% solution such that the new concentration is 35%. What is the fraction of the solution that was replaced?
(A) 1/4
(B) 1/3
(C) 1/2
(D) 2/3
(E) ¾
My solution:
x = 40%, y = 25%, new formula "z" = 35%.
Proportion of X = |25-35| = 10
Proportion of Y = |40-35| = 5
X to Y is therefore 10 to 5. IOW, X = 2/3 of the new formula z. Therefore 1/3 of X was replaced by Y.
OA: [spoiler]1/3rd[/spoiler]
From "Tough Gmat math problems"
7. A certain quantity of 40% solution is replaced with 25% solution such that the new concentration is 35%. What is the fraction of the solution that was replaced?
(A) 1/4
(B) 1/3
(C) 1/2
(D) 2/3
(E) ¾
My solution:
x = 40%, y = 25%, new formula "z" = 35%.
Proportion of X = |25-35| = 10
Proportion of Y = |40-35| = 5
X to Y is therefore 10 to 5. IOW, X = 2/3 of the new formula z. Therefore 1/3 of X was replaced by Y.
OA: [spoiler]1/3rd[/spoiler]
