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science books

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Director
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science books [#permalink]

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New post 06 Jun 2009, 05:01
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Of the science books in a certain supply room, 50 are on botany, 65 are on zoology, 90 are on physics. 50 are on geology, and 110 are on chemistry. If science books are removed randomly from the supply room, how many must be removed to ensure that 80 of the books removed are on the same science?
(A) 81
(B) 159
(C) 166
(D) 285
(E) 324

[spoiler]OA:E[/spoiler]

Detailed explanation needed guys!
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Re: science books [#permalink]

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New post 06 Jun 2009, 09:29
Botany = 50, Zoology = 65, Physics = 90, Geology = 50, Chemistry = 110

Only Physics and Chemistry have more than 80 books. So to get the 80 books removed from same science we have to remove rest all of the which are less than 80 and than from the remaining Physics and Chemistry, one will have 80 removed and other will have 79 removed.

Total books removed = 50 + 65 + 50 + 79 + 80 = 324

Kudos [?]: 29 [0], given: 17

Director
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Joined: 25 Oct 2008
Posts: 596

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Re: science books [#permalink]

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New post 10 Jun 2009, 22:22
humans wrote:
and than from the remaining Physics and Chemistry, one will have 80 removed and other will have 79 removed.

Total books removed = 50 + 65 + 50 + 79 + 80 = 324


I did'nt understand the last part.where did the 79 come from?
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Kudos [?]: 1081 [0], given: 100

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Posts: 214

Kudos [?]: 29 [0], given: 17

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Re: science books [#permalink]

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New post 11 Jun 2009, 03:34
tejal777 wrote:
humans wrote:
and than from the remaining Physics and Chemistry, one will have 80 removed and other will have 79 removed.

Total books removed = 50 + 65 + 50 + 79 + 80 = 324


I did'nt understand the last part.where did the 79 come from?


How did 79 came? Let me try

Suppose you have 2 shelf of books, one of which contain Physics and other will have Chemistry books. Just forget about the number of books. Now you have to remove one book from each shelf and continue removing until you removed say 5 books from either of one.

Say you start removing from Physics and than Chemistry

Physics 1 2 3 4 5
Chemistry 1 2 3 4(Now don't need to remove from this one as 5 from one is already completed)

Similarly in question you was asked to remove 80 from one science so the other one left would have removed only 79. Hope this clarifies.

Kudos [?]: 29 [0], given: 17

Re: science books   [#permalink] 11 Jun 2009, 03:34
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