If 20 percent of the students at a certain college take a writing class, what percent of the students at the college take a math class?
(1) 50 percent of the students who take a writing class also take a math class.
(2) 40 percent of the students who take a math class also take a writing class.
Q: % taking Math class -> (Math class & Writing Class) + (Math class & Not Writing Class)
i) we know 20 take writing class -> 50% (20) take math class as well -> help us know how many take Math class and Writing class together -> i.e. (Math Class + Writing Class) = 10 -> Insufficient to know Math class percentage (since we don't know what math class and Not Writing Class % is)
ii) we don't know what Math class percentage is (say x). Then \(\frac{2}{5*x}\) = (Math Class + Writing Class) -> Insufficient since we don't know how many take Math Class + writing class amongst [Math class & Writing Class + Math class & Not writing Class]
Combining i) and ii) we know (Math Class + Writing Class) = 10 = \(\frac{2}{5*x}\) -> Sufficient to know x
Answer - C
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