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OG Review question pg 20 #4

Problem Solving — algebra and arithmetic (GMAT Focus Edition)
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OG Review question pg 20 #4

by shoot4greatness » Mon Jan 17, 2011 4:29 pm
Hi ya'll, I just took the quant. sample question test and there's a question that still bugs me.

Among a group of 2500 people, 35 percent invested in municipal bonds, 18 percent invest in oil stock, and 7 percent invest in both municipal bonds and oil stocks. If 1 person is to be randomly selected from the 25000 people, what is the probability that the person selected will be one who invests in municipal bonds but NOT in oil stocks?

Why do you have to subtract 7% from 35%? Is it because7% who invested in both constitute a part of the 35% of municipal bonds?
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by 4GMAT_Mumbai » Mon Jan 17, 2011 9:50 pm
Hi,

Yes - That is right ...

People who invested in both = 7%

People who invested in Muni and not in oil = 35 - 7 = 28%

People who invested in oil and not in Muni = 18 - 7 = 11%

People who invested in at least one of the two = 35 + 18 - 7 = 46%
Naveenan Ramachandran
4GMAT, Dadar(W) & Ghatkopar(W), Mumbai
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by shoot4greatness » Mon Jan 17, 2011 10:10 pm
thank you 4GMAT_Mumbai,

As I was going through the problems, it became apparent that unless the problem specifically states "only", you have to subtract the possibility of both occurance from a, but not b or b but not a. The 7% overlaps between 35 and 18. Thank you again for confirmation. Fight on!!!
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