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10 Jan 2006, 17:06
Kudos
Bookmarks
Hi 
I have found those formula about restricted permutations
does this make sense to anyone ?
plz provide examples so that we can all learn and understand when to apply them
hope it help
thanks
Restricted – Permutations
(a) Number of permutations of ‘n’ things, taken ‘r’ at a time, when a particular thing is to be always included in each arrangement
= r n-1 Pr-1
(b) Number of permutations of ‘n’ things, taken ‘r’ at a time, when a particular thing is fixed: = n-1 Pr-1
(c) Number of permutations of ‘n’ things, taken ‘r’ at a time, when a particular thing is never taken: = n-1 Pr.
(d) Number of permutations of ‘n’ things, taken ‘r’ at a time, when ‘m’ specified things always come together = m! x ( n-m+1) !
(e) Number of permutations of ‘n’ things, taken all at a time, when ‘m’ specified things always come together = n ! - [ m! x (n-m+1)! ]
I have found those formula about restricted permutations
does this make sense to anyone ?
plz provide examples so that we can all learn and understand when to apply them
hope it help
thanks
Restricted – Permutations
(a) Number of permutations of ‘n’ things, taken ‘r’ at a time, when a particular thing is to be always included in each arrangement
= r n-1 Pr-1
(b) Number of permutations of ‘n’ things, taken ‘r’ at a time, when a particular thing is fixed: = n-1 Pr-1
(c) Number of permutations of ‘n’ things, taken ‘r’ at a time, when a particular thing is never taken: = n-1 Pr.
(d) Number of permutations of ‘n’ things, taken ‘r’ at a time, when ‘m’ specified things always come together = m! x ( n-m+1) !
(e) Number of permutations of ‘n’ things, taken all at a time, when ‘m’ specified things always come together = n ! - [ m! x (n-m+1)! ]
Archived Topic
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This topic has been closed and archived due to inactivity or violation of community quality standards. No more replies are possible here.
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10 Jan 2006, 23:50
Kudos
Bookmarks
I'm not sure you want to memorise so many formulas when you would already be under a lot of mental stress during the GMAT. I would recommend you see the logic behind the probabiltiy question, and work out the solution using simple permutation equations. So far, I have not seen a restricted case where I have to recall a formula off-hand. Go through all the combinatorics question in this forum and you'll see what I mean. :wink:
Archived Topic
Hi there,
This topic has been closed and archived due to inactivity or violation of community quality standards. No more replies are possible here.
Where to now? Join ongoing discussions on thousands of quality questions in our Quantitative Questions Forum
Still interested in this question? Check out the "Best Topics" block above for a better discussion on this exact question, as well as several more related questions.
Thank you for understanding, and happy exploring!
