The given question is a GMAT 600 level problem solving question from Mixtures & Alligation. This GMAT sample question tests the concept of computing the ratio in which two liquids should be mixed. An ideal question to apply the Rule of Alligation to compute the ratio in which two individual components of a mixture should be mixed.

Question 4: In what ratio should a 20% methyl alcohol solution be mixed with a 50% methyl alcohol solution so that the resultant solution has 40% methyl alcohol in it?

1. 1 : 2
2. 2 : 1
3. 1 : 3
4. 3 : 1
5. 2 : 3

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Video Explanation

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Explanatory Answer | GMAT Mixtures Alligation Q4

Method 1: Using Linear Equations

Let x litres of 20% methyl alcohol solution be mixed with y litres 50% methyl alcohol solution.
If we find the values of x and y, we have found the ratio in which the two liquids are mixed.

	Volume	Volume of Methyl Alcohol
20% Solution	x litres	0.2x
50% Solution	y litres	0.5y
Final mixture	x + y litres	0.4(x + y)

The volume of methyl alcohol found in the final mixture is the sum of the volumes of methyl alcohol in the 20% and 50% solutions.
0.4x + 0.4y = 0.2x + 0.5y
Or 0.2x = 0.1y
Or \\frac {x} {y}) = \\frac {0.1} {0.2})
So, the ratio x : y = 1 : 2

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Method 2: Using Alligations

Choice A is the correct answer.