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# James's library contains reference, biography, and fiction books only,

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Math Expert
Joined: 02 Sep 2009
Posts: 55639
James's library contains reference, biography, and fiction books only,  [#permalink]

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12 Dec 2018, 01:44
00:00

Difficulty:

5% (low)

Question Stats:

89% (00:41) correct 11% (00:34) wrong based on 43 sessions

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James's library contains reference, biography, and fiction books only, in the ratio of 1:2:7, respectively. If James's library contains 30 books, how many biographies does he own?

A. 2
B. 3
C. 4
D. 6
E. 10

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Re: James's library contains reference, biography, and fiction books only,  [#permalink]

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12 Dec 2018, 01:54
Bunuel wrote:
James's library contains reference, biography, and fiction books only, in the ratio of 1:2:7, respectively. If James's library contains 30 books, how many biographies does he own?

A. 2
B. 3
C. 4
D. 6
E. 10

total : 10 in ratio

so Biography : 10x/2= 30

x= 6 IMO D
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Joined: 04 Jan 2015
Posts: 2888
Re: James's library contains reference, biography, and fiction books only,  [#permalink]

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12 Dec 2018, 01:56

Solution

Given:
• James's library contains reference, biography, and fiction books only, in the ratio of 1:2:7, respectively.
• In James’s library, there are 30 books in total.

To find:
• The number of biographies that James owns.

Approach and Working:
As the ratio of reference, biography and friction is 1: 2: 7, the number of biographies = $$30 * \frac{2}{1+2+7} = 30 * \frac{2}{10} = 6$$
Hence, the correct answer is option D.

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Re: James's library contains reference, biography, and fiction books only,  [#permalink]

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28 Dec 2018, 12:20
Employ the unknown multiplier technique in this case to find that x = 3.

7x + 2x + 1x = 30
x = 3

2(3) = 6

So 6 biographies.
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Re: James's library contains reference, biography, and fiction books only,   [#permalink] 28 Dec 2018, 12:20
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