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vineetbatra
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Post subject: Jefferson School Sets - Matrix did not work  Posted: Fri Jan 15, 2010 12:19 am |
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Posts: 24
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Hello,
I tried to solve this question using the matrix table but cannot find the correct answer.
Thanks,
Vineet
The Matrix I build is as follows:
F NF Total
S ? ? 240
NS ? ? 60
Total 300 100 300
OA is D I get E
In Jefferson School, 300 students study French or Spanish or both. If 100 of these students do not study French, how many of these students study both French and Spanish?
(1) Of the 300 students, 60 do not study Spanish.
(2) A total of 240 of the students study Spanish.
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karmaresh15
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Post subject: Re: Jefferson School Sets - Matrix did not work Posted: Fri Jan 15, 2010 5:03 am |
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Hi Vineet .. Please look at the sentence carefully. In Jefferson School, 300 students study French or Spanish or both.The hidden information is that the number of students who don't read either spanish or french is 0. Taking case I .. The matrix would be Code:
F not F Total
S
not S 0 60
Total 100 300
I think you can easily find out that number of students reading both french and spanish is 140. Taking case II .. The matrix would be Code:
F not F Total
S 240
not S 0
Total 100 300
Again you can find out that number of students reading both french and spanish is 140. Hence in each of the cases above you can find out the required information. So, D
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vineetbatra
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Post subject: Re: Jefferson School Sets - Matrix did not work Posted: Fri Jan 15, 2010 9:45 am |
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Thats a great spot, I just completly missed that point.
Thanks,
Vineet
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karmaresh15
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Post subject: Re: Jefferson School Sets - Matrix did not work Posted: Fri Jan 15, 2010 3:54 pm |
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vineetbatra wrote: Thats a great spot, I just completly missed that point.
Thanks,
Vineet You are welcome :)
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esledge
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Post subject: Re: Jefferson School Sets - Matrix did not work Posted: Wed Jan 20, 2010 2:43 pm |
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| ManhattanGMAT Staff |
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Posts: 903
Location: St. Louis, MO
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Great catch, karmaresh15.
The general rule is that the Double-Set Matrix is preferable to the Venn Diagram for 2 category scenarios. This is the only exception I've seen: 0 in the non-A/non-B category. In a Venn diagram, the 0 would go outside both circles, in the area most people ignore anyway.
_________________
Emily Sledge
Instructor
ManhattanGMAT
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accounts
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Post subject: Re: Jefferson School Sets - Matrix did not work Posted: Wed Sep 15, 2010 3:48 am |
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Posts: 9
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I kind of disagree to
The hidden information is that the number of students who don't read either spanish or french is 0.
We cannot make such an assumption especially in DS.
S NOT S TOTAL
French x y
not F z w
they question is telling us x+y+z = 300 (In Jefferson School, 300 students study French or Spanish or both)
It does not clearly mention that w number of students do not study either.
On a problem solving such an approach is fine but not on DS.
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gokul_nair1984
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Post subject: Re: Jefferson School Sets - Matrix did not work Posted: Wed Sep 15, 2010 7:02 am |
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accounts wrote: I kind of disagree to
The hidden information is that the number of students who don't read either spanish or french is 0.
We cannot make such an assumption especially in DS. @accounts: You are wrong;you are not assuming anything but uncovering indirectly mentioned facts (especially in DS set theory and overlapping set theory questions)accounts wrote: It does not clearly mention that w number of students do not study either. It has to be understood. They do not need to state everything explicitly; some information has to be alluded.
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RonPurewal
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Post subject: Re: Jefferson School Sets - Matrix did not work Posted: Thu Sep 16, 2010 7:57 am |
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| ManhattanGMAT Staff |
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Posts: 6765
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accounts wrote: I kind of disagree to
The hidden information is that the number of students who don't read either spanish or french is 0.
We cannot make such an assumption especially in DS.
S NOT S TOTAL
French x y
not F z w
they question is telling us x+y+z = 300 (In Jefferson School, 300 students study French or Spanish or both) yeah, but, when you write the number 300 in the lower right corner of this matrix, you are committing yourself to only considering the three quantities represented by x, y, and z. in other words, the entire universe of this problem consists of the students who take french or spanish (or both). we are free to ignore students who take neither, and thus to place a 0 in the corresponding box.
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