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There are 7 Physics and 1 chemistry book in shelf A

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PiyushK
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There are 7 Physics and 1 chemistry book in shelf A [#permalink] New post   Updated on: 06 Aug 2013, 05:24
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88% (01:16) correct 12% (01:57) wrong based on 153 sessions
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There are 7 Physics and 1 Chemistry book in shelf A and 5 Physics books in Shelf B, one book is moved from shelf A to shelf B. A student picks up a book from shelf B. Find the probability that the Chemistry book is taken by the student.

A. 7/8
B. 1/8
C. 1/48
D. 5/48
E. 5/6
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C

Originally posted by PiyushK on 06 Aug 2013, 02:14.
Last edited by Zarrolou on 06 Aug 2013, 05:24, edited 1 time in total.
Edited the question.
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Re: There are 7 Physics and 1 chemistry book in shelf A [#permalink] New post   06 Aug 2013, 05:28
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I)Probability that the book moved from A to B is Chemistry=\(\frac{1}{8}\).
II)Probability that the boom taken from B is Chemistry=\(\frac{1}{6}\).

\(P=\frac{1}{8}*\frac{1}{6}=\frac{1}{48}\).

C
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Re: There are 7 Physics and 1 chemistry book in shelf A [#permalink] New post   06 Aug 2013, 05:41
Consider moving of the 1 book from shelf A to shelf B as the 1st event that is followed by student picking a book from shelf B as the second event.

P(Student picking a chemistry book from shelf B) = P(Moving a chemistry book from shelf A to shelf B) * P(Student picking a chemistry book from shelf B)
= 1/8* 1/6 ( There are total 8 books of which 1 is chemistry book and after the move, there will be 1 chemistry book in the new number of books (6) in shelf B)
= 1/48

Hence answer is C

Hope this helps.
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Re: There are 7 Physics and 1 chemistry book in shelf A [#permalink] New post   02 Apr 2015, 11:58
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Hi All,

The probability math in this prompt is relatively simple, but the answer choices are written in such a way that you can avoid most of the math entirely.

The calculation in this question involves 2 steps:

1) The chemistry book has to get from Shelf A to Shelf B
2) A student has to randomly pick the chemistry book from Shelf B

Since there are 8 books on Shelf A, there is a 1/8 chance of the chemistry book making it to Shelf B. Since the second step then has to occur, the overall probability MUST be far less than 1/8.

Looking at the answers, there are two that are less than 1/8, but one of them (5/48) is really close to 1/8 so it can't be the answer. We need an answer that is significantly smaller than 1/8 and there's only 1 option that fits....

Final Answer:
Show Spoiler
C


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Re: There are 7 Physics and 1 chemistry book in shelf A [#permalink] New post   01 Jan 2022, 07:16
Hello from the GMAT Club BumpBot!

Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

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Re: There are 7 Physics and 1 chemistry book in shelf A [#permalink]
01 Jan 2022, 07:16
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