GMAT Prep Exam 2 - Survey married/self-employed

[Guest]

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!

[jimbo]

Just simplyfiy: 31/248 (248/31=8). 31/248 = 1/8

[RonPurewal]

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.

[guest612]

so close yet so far.

[StaceyKoprince]

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.

[PC]

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

[RonPurewal]

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.