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# There are 4 books on physics and 2 books on maths.Find the

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Intern
Joined: 29 Aug 2003
Posts: 29
Location: Mumbai
There are 4 books on physics and 2 books on maths.Find the [#permalink]

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11 Dec 2003, 04:39
This topic is locked. If you want to discuss this question please re-post it in the respective forum.

There are 4 books on physics and 2 books on maths.Find the no. of ways in which these books can be arranged so that the books on maths are not together!
Director
Joined: 13 Nov 2003
Posts: 789
Location: BULGARIA

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11 Dec 2003, 04:46
6!-4!x3!=720-144=576...
Manager
Joined: 12 Oct 2003
Posts: 247
Location: USA

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11 Dec 2003, 05:01
Intern
Joined: 29 Aug 2003
Posts: 29
Location: Mumbai

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11 Dec 2003, 06:46
No..this is not the answer!!! Its 480.
I m wondering how to get 480???
Director
Joined: 13 Nov 2003
Posts: 789
Location: BULGARIA

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11 Dec 2003, 06:48
total number we can order the 6 books is 6!. When we take 4 maths together as one and the other 2 we can order these in 3! ways but for each of these orderings we will have 4! orderings of the 4 math books. Total number when maths are not together is 6!-4!x3!
Director
Joined: 13 Nov 2003
Posts: 789
Location: BULGARIA

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11 Dec 2003, 06:53
Sorry but I got it other way round, i calculated for 4 mats and 2 physics. . when it is 4 physics and 2 maths it should be 6!-5!x2=720-240=480
Manager
Joined: 12 Oct 2003
Posts: 247
Location: USA

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11 Dec 2003, 06:55
there are 4 PHYSICS books and not math books.

using BG's CORRECT LOGIC ...

2 math books as 1 + 4 other books = 5!
2 math books can be arranged in 2! = 2 ways
# of ways which have 2 math books together = 5! * 2 = 120 * 2 = 240
# of total ways = 6! = 720

# of ways which DON'T have the 2 math books together = 720 - 240 = 480
Manager
Joined: 12 Oct 2003
Posts: 247
Location: USA

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11 Dec 2003, 06:56
well was typing when BG already posted his correction! so you can ignore my post
CEO
Joined: 15 Aug 2003
Posts: 3454

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13 Dec 2003, 00:20
4128851 wrote:
There are 4 books on physics and 2 books on maths.Find the no. of ways in which these books can be arranged so that the books on maths are not together!

total # of ways of arranging these "distinguishable" books

6! = 720

ways in which math books are ALWAYS together.

5! *2! =240

required # of ways = 720 - 240 = 480
Re: Probability!!!   [#permalink] 13 Dec 2003, 00:20
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