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junii
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In a certain library, the number of books on History is double the num 19 Jun 2021, 23:44
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77% (02:46) correct 23% (03:06) wrong based on 60 sessions

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In a certain library, the number of books on History is double the number of books on Philosophy, and the number of books on Psychology is triple the number of books on history. A new set of books on History, Philosophy, and Psychology comes to the library such that the ratio of the number of books on the Philosophy to the books on History becomes four times and the ratio of the number of books on History to the number of books on Psychology becomes five times. What is the new ratio of the number of books on Philosophy to History to Psychology?

A. 3: 5: 10
B. 5:3:10
C. 10:5:3
D. 8:4:3
E. 3:4:8

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In a certain library, the number of books on History is double the num 23 Jun 2021, 22:48
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Bunuel pls can you explain this question. thanks
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In a certain library, the number of books on History is double the num 23 Jun 2021, 23:11
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In a certain library, the number of books on History is double the number of books on Philosophy, and the number of books on Psychology is triple the number of books on history. A new set of books on History, Philosophy, and Psychology comes to the library such that the ratio of the number of books on the Philosophy to the books on History becomes four times and the ratio of the number of books on History to the number of books on Psychology becomes five times. What is the new ratio of the number of books on Philosophy to History to Psychology?

A. 3: 5: 10
B. 5:3:10
C. 10:5:3
D. 8:4:3
E. 3:4:8
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"the number of books on History is double the number of books on Philosophy"
Phil:His = 1:2

"the number of books on Psychology is triple the number of books on history"
His:Psych = 1:3

New books arrive so that
Phil:His ratio becomes 4 times so new ratio = 4:2 = 2:1 = 10:5
and His:Psych becomes 5 times so new ratio = 5:3

So Phil:His:Psych = 10:5:3

Answer (C)
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In a certain library, the number of books on History is double the num 24 Jun 2021, 00:58
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Let p be the number of Philosophy books, h be the number of History books and s be the number of Psychology books before the addition.

Therefore, h = 2p or h:p = 2:1 and s = 3h or s:h = 3:1

Let P be the number of philosophy books, H be the number of History books and S be the number of Psychology books after the addition.

The new ratio of Philosophy books to History books becomes 4 times. Original ratio of philosophy to history = p:h = 1:2.
Therefore, new ratio of Philosophy to history = P:H = 4 * (\(\frac{1}{2}\)) = 2; i.e. P:H = 2:1

The new ratio of History books to Psychology books becomes 5 times. Original ratio of history to psychology books = h:s = 1:3
Therefore, new ratio of History to Psychology = H:S = 5 * (\(\frac{1}{3}\)) = \(\frac{5 }{ 3}\); i.e. H:S = 5:3.

The new ratio of Philosophy, History and Psychology books can be obtained by bridging the two new ratios, giving P:H:S = 10:5:3.

The correct answer option is C.

Hope that helps!
Aravind BT

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