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venn diagram help!!

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venn diagram help!!

by jamiegirl » Mon Jul 18, 2011 11:33 am
I'm just starting to study for the GMAT and I totally forgot how to utilize venn diagrams. I'm pretty sure I would use one in this situation I'm just not positive....

1. Of 200 students taking the GMAT, all of them have college degrees, 120 have been out of college for at least 3 years, 70 have business degrees, and 60 have been out of college for less than 3 years and do not have business degrees. How many of them have been out of college for at least 3 years and have business degrees.

(A) 40
(B) 50
(C) 60
(D) 70
(E) 80

please and thank you!!
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by winniethepooh » Mon Jul 18, 2011 11:47 am
Out of 200 people taking Gmat:
1)120 = Out since at least 3 years and (some have business degrees = ?)-- this is what we have to find.
2)60 = Out of college since less than 3 years but do not have business degrees.
3)70 = have business degrees.

There is surely nothing common in 1) and 2)
Our solution is to find the common between 1) and 3).
200 - 120 - 60 - 70 = -[50]{As these additional 50 students can't comprise of 1) and 2) they are the intersection of 1) and 3).
Hence, B.
Last edited by winniethepooh on Mon Jul 18, 2011 12:11 pm, edited 1 time in total.
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by BenchPrepGURU » Mon Jul 18, 2011 11:59 am
Actually, a Venn diagram is not a good idea in this situation. Because the categories are mutaully exclusive, you should use a table. I've inserted a table below as an image - If you click on it it will enlarge.


Image

Note that you don't have to fill in the table completely in order to find the correct answer, which is B. I'm not really sure what winniethepooh's reasoning is, but it's a perfect example for what can happen when you use a Venn diagram where it's not appropriate.

BenchPrepGURU
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by winniethepooh » Mon Jul 18, 2011 12:10 pm
That was a typo(corrected now).
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