damilolaamele wrote:Hi All,
Found this question and was wondering whether I could apply the ratios principle to solve it.
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
Ans is B
To determine the ratio of the two solutions, use ALLIGATION.
Step 1: Plot the 3 percentages on a number line, with the two starting percentages (40% and 25%) on the ends and the goal percentage (35%) in the middle.
40%----------35%----------25%
Step 2: Calculate the distances between the percentages.
40%----
5----35%----
10----25%
Step 3: Determine the ratio in the mixture.
The ratio of 40% solution to 25% solution is the RECIPROCAL of the distances in red.
(40% solution) : (25% solution) = 10:5 = 2:1.
Since 2+1 = 3, of every 3 liters, 2 liters must be the original 40% solution and 1 liter must be the 25% solution.
Thus:
(25% solution)/total = 1/3.
The correct answer is
B.
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