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# M01-Q15

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VP
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16 Jul 2008, 21:25
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At Daifu university, 40% of all students are both members of a student organization and want to reduce their tuition costs. 20% of those students who want to reduce tuition are not members of the student organization. What percentage of all Daifu students want to reduce tuition?

(A) 20%
(B) 30%
(C) 40%
(D) 50%
(E) 60%

Source: GMAT Club Tests - hardest GMAT questions

REVISED VERSION OF THIS QUESTION IS HERE: m01-q15-67289.html#p1103452
Director
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17 Jul 2008, 22:24
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my 2 cents, practise venn diagram and always use it .... its more visual than grid and it makes me more confident about the right answer.

for this question

we need to find out (40+x)

and its given that (40+x) * 20/100 = x
x = 10

Attachment:

venn1.JPG [ 8.19 KiB | Viewed 11295 times ]
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11 Jul 2012, 05:17
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Expert's post
goalsnr wrote:
At Daifu university, 40% of all students are both members of a student organization and want to reduce their tuition costs. 20% of those students who want to reduce tuition are not members of the student organization. What percentage of all Daifu students want to reduce tuition?

(A) 20%
(B) 30%
(C) 40%
(D) 50%
(E) 60%

[Reveal] Spoiler: OA
D

Source: GMAT Club Tests - hardest GMAT questions

Can Someone please explain how to solve the above Question? I could'nt getmuch help from the OE.

Below is revised version of this question.

At Daifu university, 40% of all students are members of both a chess club and a swim team. If 20% of members of the swim team are not members of the chess club, what percentage of all Daifu students are members of the swim team?

A. 20%
B. 30%
C. 40%
D. 50%
E. 60%

Assume there are total of 100 students. 40 students are members of both clubs. We are told that: "20% of members of the swim team are not members of the chess club", thus if S is a # of members of the swim team then 0.2S is # of members of ONLY the swim teem:

40+0.2S=S --> S=50.

Or another way: since "20% of members of the swim team are not members of the chess club" then the rest 80% of members of the swim team (S) ARE members of the chess club, so members of both clubs: 0.8*S=40 --> S=50.

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Director
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16 Jul 2008, 21:31
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This is good example of grid question.
Attachments

Grid.doc [25 KiB]

Senior Manager
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30 Jul 2011, 00:33
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oops.. I chose 60. Guess it's a common mistake.
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17 Jul 2008, 21:42
Thanks.
How do we need decide when to use sets and when to use grid?
Manager
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19 Jul 2008, 00:56
True , for 2 sets I think Venn is the best way to go. For more than 2 grid makes things relatively simpler.
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13 Sep 2008, 11:20
durgesh79 wrote:
my 2 cents, practise venn diagram and always use it .... its more visual than grid and it makes me more confident about the right answer.

for this question

we need to find out (40+x)

and its given that (40+x) * 20/100 = x
x = 10

Attachment:
venn1.JPG

durgesh for PRESIDENT....
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29 Jul 2009, 10:51
seems like question has changed a little.

Anyway, posting the latest question:
At Daifu university, 40% of all students are members of both a chess club and a swim team. If 20% of members of the swim team are not members of the chess club, what percentage of all Daifu students are members of the swim team?

The solution provided assumes that the students are either member of chess club or swim team or both. But no where in the question this has been mentioned.
I found it difficult to solve, since I didn't know how many students are member of neither of these clubs
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01 Oct 2009, 21:46
irajeevsingh wrote:
True , for 2 sets I think Venn is the best way to go. For more than 2 grid makes things relatively simpler.

Is there a question on the GMATClub tests that uses 3 or more sets so I can practice the larger grid? So far I've always used Venn diagrams for solving these kinds of problems.
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28 Jan 2010, 15:39
Can anyone explain the answer for this ?

At Daifu university, 40% of all students are members of both a chess club and a swim team. If 20% of members of the swim team are not members of the chess club, what percentage of all Daifu students are members of the swim team?

20 %

30 %

40 %

50 %

60 %
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FEB 15 2010 !!

well I would not disturb you after the D-day ..so please !!!

It Will Snow In Green , One Day !!!!

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05 Jul 2010, 06:33
Snowingreen wrote:
Can anyone explain the answer for this ?

At Daifu university, 40% of all students are members of both a chess club and a swim team. If 20% of members of the swim team are not members of the chess club, what percentage of all Daifu students are members of the swim team?

20 %

30 %

40 %

50 %

60 %

Hi Snowingreen,

The Answer here also is same D as this is a similar question as above.
Just replace "Members of student organization" with "members of chess club" and "students who want to reduce tuition fees" with "Members of swim club". Then refer Durgesh79's explanation above.
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+1 kudos me if this is of any help...

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07 Jul 2011, 09:57
IMO D.

We can easily rule out the first 3 options..I did not use the grid but it seems a viable option..
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08 Jul 2011, 10:52
The updated question is much clearer.

D it is..

% S (who only Swim) = (20/100) * ( .4 + S)

only S = 10.

Total S = 10 + 40 = 50
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24 Sep 2011, 18:18
bigoyal wrote:
seems like question has changed a little.

Anyway, posting the latest question:
At Daifu university, 40% of all students are members of both a chess club and a swim team. If 20% of members of the swim team are not members of the chess club, what percentage of all Daifu students are members of the swim team?

The solution provided assumes that the students are either member of chess club or swim team or both. But no where in the question this has been mentioned.
I found it difficult to solve, since I didn't know how many students are member of neither of these clubs

How to solve this using 2 x 2 grid?
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14 Jan 2012, 22:12
if 20 % of swim club are not the member of chess then 80 % are member of chess.

Assume swim club has x members - then .8x = 40 solve for x you get x = 50 which makes the percentage of members overall in swim club as 50 %

IMO D
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13 Jul 2012, 03:52
I will try creating a grid here

Student org No Student Org Total
Reduce Cost 40 x (40+x)

No Reduce Cost

Total 100

Now, says 20% of those who want to reduce cost are not part of student org
So, 20%( 40+x)=x => 80+2x =10x => x=10

so total number of students who want to reduce tuition is 40+x = 40+10=50

Manager
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22 Jul 2012, 09:33
Followed the grid method. Set up the grid correctly but used two variables instead of one. That led to taking more time. Good question with percentages on grid.

Concluded with D but since messed up the variables took abt a min more.
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02 May 2013, 12:59
bunuel- u rock...
wat a simple expl.
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26 Jun 2014, 06:30
You don't need grid to solve these kind of problems. Solve it using venn.
Re: M01-Q15   [#permalink] 26 Jun 2014, 06:30

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# M01-Q15

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