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# In a certain collection of books there are 30 books (m25#21)

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CIO
Joined: 02 Oct 2007
Posts: 1218
In a certain collection of books there are 30 books (m25#21) [#permalink]

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15 Feb 2012, 06:53
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In a certain collection of books there are 30 books in hard cover that contain more than 100 pages. If 15 percent of the books that contain more than 100 pages are in hard cover, how many books contain more than 100 pages but are not in hard cover?

(A) 60
(B) 90
(C) 170
(D) 180
(E) 200
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Manager
Joined: 30 Jul 2011
Posts: 117
Location: United States (NJ)
Concentration: General Management, Finance
GMAT 1: 520 Q40 V21
GPA: 2.95
Re: In a certain collection of books there are 30 books (m25#21) [#permalink]

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30 Mar 2012, 20:36
1
KUDOS
I setup a simple proportion for this:

15% of all the books are hardcover and over 100 pages. This number was 30.

So what we're trying to find out right now is $$x$$, which is the total number of books.

$$15/100 = 30/x$$

$$x = 200$$

But now we have to subtract 30 from this, because we are trying to find the number of books that are only over 100 pages.

Senior Manager
Joined: 13 Mar 2012
Posts: 358
Concentration: Operations, Strategy
Re: In a certain collection of books there are 30 books (m25#21) [#permalink]

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01 Apr 2012, 20:30
1
KUDOS
dzyubam wrote:
In a certain collection of books there are 30 books in hard cover that contain more than 100 pages. If 15 percent of the books that contain more than 100 pages are in hard cover, how many books contain more than 100 pages but are not in hard cover?

(A) 60
(B) 90
(C) 170
(D) 180
(E) 200

total hard cover books> 100 pages = 30
let total books>100 pages=x

then 0.15x=30
=> x=200

hence 200-30=170 =no. of books>100 pages but no hard cover

hence C
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Manager
Joined: 24 Apr 2013
Posts: 53
Schools: Duke '16
Re: In a certain collection of books there are 30 books (m25#21) [#permalink]

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20 May 2013, 18:51
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restore wrote:
I setup a simple proportion for this:

15% of all the books are hardcover and over 100 pages. This number was 30.

So what we're trying to find out right now is $$x$$, which is the total number of books.

$$15/100 = 30/x$$

$$x = 200$$

But now we have to subtract 30 from this, because we are trying to find the number of books that are only over 100 pages.

This is an EXCELLENT EXPLANATION!!! VERY Simple and straight foward thanks
Re: In a certain collection of books there are 30 books (m25#21)   [#permalink] 20 May 2013, 18:51
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# In a certain collection of books there are 30 books (m25#21)

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