Official Guide DS#89

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Official Guide DS#89

#89 OG
The question is not asking for a % or an actual #. It’s asking for a relational…giving some % information. Let’s take a look.

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Is the number of members of Club X greater than the number of members of Club Y?

(1) Of the members of Club X, 20 percent are also members of Club Y
(2) Of the members of Club Y, 30 percent are also members of Club X

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GMATPill Explanation
As we write out the expressions, we start to see that there is an overlap of members.
20%(ClubX) => Are in ClubY
30%(ClubY) => Are in Club X

Each statement alone has too many unknowns and just one equation. We know that 20% of ClubX members are in ClubY but we don’t know that actual number.

What if we combine them? Hm, well when combined, we come to realize that the overlapping members must be the same number. They are referring to the same thing.

20%(ClubX) = 30%(ClubY)
0.2ClubX = 0.3ClubY
Club X = (0.3/0.2)*ClubY
ClubX = 1.5(ClubY)
We have a relational equation here…ClubX is 1.5 times greater than ClubY. Question solved. Answer used both statements 1 and 2, so it is C.

GMATPill vs Official Guide Explanation

Now, if you were to get an explanation from the Official Guide book itself, notice the difference in explanation depth and attack strategy compared to GMATPill’s explanation above. According to most students, the official guide explanations don’t really give them a good enough thought process to attack the question. And sometimes, it’s just difficult to follow.

For many students, the GMATPill explanation works a lot better.

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