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40% of the students at a school take a math class and 60% of

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40% of the students at a school take a math class and 60% of

by Max@Math Revolution » Tue May 08, 2018 1:41 am

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[GMAT math practice question]

40% of the students at a school take a math class and 60% of the school's students take a physics class. What percent of students at the school take a math class, but not a physics class?

1) 25% of students take both a math class and a physics class.
2) 25% of students take a physics class, but do not take a math class.
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Source: — Data Sufficiency |
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by Max@Math Revolution » Wed May 09, 2018 11:49 pm

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Forget conventional ways of solving math questions. For DS problems, the VA (Variable Approach) method is the quickest and easiest way to find the answer without actually solving the problem. Remember that equal numbers of variables and independent equations ensure a solution.

This is a typical 2 x 2 matrix question with percentages. To solve it, we need 3 percentages. The original condition provides 2 percentages, so we need only 1 more percentage. Each of the conditions provides 1 percentage, so the VA method tells us that, each condition is likely to be sufficient.

Therefore, D is the answer.
Answer: D
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