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In a group of 80 college students, how many own a car?

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In a group of 80 college students, how many own a car? [#permalink] New post 16 Apr 2011, 06:39
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In a group of 80 college students, how many own a car?

(1) Of the students who do not own a car, 14 are male.
(2) Of the students who own a car, 42% are female.

OPEN DISCUSSION OF THIS QUESTION IS HERE: in-a-group-of-80-college-students-how-many-own-a-car-95019.html
[Reveal] Spoiler: OA

Last edited by Bunuel on 29 Mar 2014, 10:48, edited 1 time in total.
Edited the question.
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Re: Wrong Q - DS [#permalink] New post 16 Apr 2011, 06:44
how can it be deduced from 2 stmt.
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Re: Wrong Q - DS [#permalink] New post 16 Apr 2011, 08:31
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gmatprep2011 wrote:
In a group of 80 college students, how many own a car?

(1) Of the students who do not own a car, 14 are male.

(2) Of the students who own a car, 42% are female.


Official Answer is B...

Shouldnt the answer be E...


B is correct!!

Let a and b are the number of students who own and do not own a car resp. We need to find the value of B.
Also a+b = 80
Statemen1 : not sufficient.

Statement 2: 42% of a = female => 42a/100 = female = 21a/50.

Now here is the trick !! number of females must be an integer. => a must have minimum value of 50.

if a = 50 => females = 21. a can not be 100 as total is 80

=> a has to be 50. Hence B
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Re: Wrong Q - DS [#permalink] New post 16 Apr 2011, 09:36
gurpreetsingh wrote:
gmatprep2011 wrote:
In a group of 80 college students, how many own a car?

(1) Of the students who do not own a car, 14 are male.

(2) Of the students who own a car, 42% are female.


Official Answer is B...

Shouldnt the answer be E...


B is correct!!

Let a and b are the number of students who own and do not own a car resp. We need to find the value of B.
Also a+b = 80
Statemen1 : not sufficient.

Statement 2: 42% of a = female => 42a/100 = female = 21a/50.

Now here is the trick !! number of females must be an integer. => a must have minimum value of 50.

if a = 50 => females = 21. a can not be 100 as total is 80

=> a has to be 50. Hence B


The value of 'a' can be zero as well, at least mathematically as that would also justify above conditions. Of course, that makes the statement 2 a tad impractical, but still correct mathematically. So, the value of 'a' can not be ascertained for sure and the answer should still be E.

A bit of an ambiguous question for sure. Maybe the questions needs to mention that a and b are non-zero or something.
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Re: Wrong Q - DS [#permalink] New post 16 Apr 2011, 10:48
a can not be zero.

if a is zero, how can 42% of it be females?

think again !!
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Re: Wrong Q - DS [#permalink] New post 16 Apr 2011, 16:30
It can be 0 and then 42% of the same would also be 0 (number of females). Where does it say in the question that number of females have to be non-zero. All we know is that females = 0.42*a and this equation can be valid at both a = 0 and a = 50 without contradicting anything given in the question.

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Re: Wrong Q - DS [#permalink] New post 16 Apr 2011, 20:07
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beyondgmatscore wrote:
It can be 0 and then 42% of the same would also be 0 (number of females). Where does it say in the question that number of females have to be non-zero. All we know is that females = 0.42*a and this equation can be valid at both a = 0 and a = 50 without contradicting anything given in the question.


(2) Of the students who own a car, 42% are female.

The phrase 'Of the students who own a car' already tells you that some students own a car, so it is not a possibility that 0 students own a car. Further, if I were to tell you that 0 people own a car, and I asked you what percentage of the students who own a car are female, you would not say "42%". It would be meaningless to assign a percentage in that case. The GMAT would never tell you '42% of people own a car' and then make the 'trap' that 0 people might own a car, because most test takers would, very reasonably, assume the number of car owners needs to be non-zero.

So if you see a phrase like '1/3 of the people in North America who own a computer are Canadian' or '45% of the marbles in a bag are green', you can certainly assume that the number of North Americans who own a computer, or the number of marbles in the bag, is not zero.
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Re: Wrong Q - DS [#permalink] New post 16 Apr 2011, 20:18
Ian very nice explanation.

beyondgmatscore: I advice you not to assume too much on GMAT. DS would be hard to crack if you make such assumptions.
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Re: Wrong Q - DS [#permalink] New post 16 Apr 2011, 23:51
Thanks Ian and Gurpreet.
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Re: In a group of 80 college students, how many own a car? (1) [#permalink] New post 29 Mar 2014, 10:31
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Re: In a group of 80 college students, how many own a car? [#permalink] New post 29 Mar 2014, 10:48
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In a group of 80 college students, how many own a car?

(1) Of the students who do not own a car, 14 are male. Clearly insufficient.

(2) Of the students who own a car, 42% are female --> let # of students who own a car be x --> 0.42x= # of females who own a car. But 0.42x must be an integer, as it represent # of females. 0.42x=integer --> \frac{21}{50}x=integer --> x is a multiple of 50: 50, 100, 150, ... But x (# of students who own car) must also be less than (or equal to) 80. So x=50. sufficient.

Answer: B.

OPEN DISCUSSION OF THIS QUESTION IS HERE: in-a-group-of-80-college-students-how-many-own-a-car-95019.html
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Re: In a group of 80 college students, how many own a car?   [#permalink] 29 Mar 2014, 10:48
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