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GMAT Prep Exam 2 - Survey married/self-employed

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Guest
 Post subject: GMAT Prep Exam 2 - Survey married/self-employed
 Post Posted: Wed Feb 06, 2008 2:33 pm 
Please help! I can't seem to get to the right answer...

In a Survey of 248 people, 156 are married, 70 are self-employed, and 25% of those who are married are self-employed. If a person is randomly selected from those surveyed, what is the probability that the person selected will be self-employed but not married?

A- 1/8 (Right answer)
B- 4/31
C- 117/248
D-1/4
E- 31/117

I used the Double set matrix, but I get to 31/248. I don't know what I'm doing wrong!

Thank you!
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jimbo
 Post subject:
 Post Posted: Thu Feb 07, 2008 5:12 am 
Just simplyfiy: 31/248 (248/31=8). 31/248 = 1/8
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RonPurewal
 Post subject:
 Post Posted: Tue Feb 12, 2008 5:12 am 
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ManhattanGMAT Staff


Posts: 7146
by the way, when something like this happens, note it in the back of your mind: 'always check to see if i can reduce fractions before panic sets in.' could save your life - or at least a few seconds - on the real test.
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guest612
 Post subject: i did the same thing
 Post Posted: Mon Mar 17, 2008 12:40 pm 
so close yet so far.
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StaceyKoprince
 Post subject:
 Post Posted: Mon Mar 17, 2008 5:00 pm 
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ManhattanGMAT Staff


Posts: 6069
Location: San Francisco
yes - it's so frustrating when that happens! You could also try to estimate in order to pick something close to your answer, as the answer choices have some spread.

_________________
Stacey Koprince
Instructor
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ManhattanGMAT
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PC
 Post subject:
 Post Posted: Mon Mar 24, 2008 6:57 pm 
Can someone please let me know how this probability is arrived at . I think I may be missing something , I am getting only 26/248
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RonPurewal
 Post subject:
 Post Posted: Sat Mar 29, 2008 12:35 am 
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ManhattanGMAT Staff


Posts: 7146
PC wrote:
Can someone please let me know how this probability is arrived at . I think I may be missing something , I am getting only 26/248


you're looking for people who are SE but not M. that's a subset of people who are SE, so you should consider that set to get some insight.
the set of people who are SE has two subsets:
* people who are SE and M
* people who are SE but not M

there are a total of 70 who are SE.
the # who are both SE and M is 25% of the total number of M: 25% of 156, or 39.
so therefore, there are 70 - 39 = 31 people who are SE but not M.
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