circular perm : GMAT Problem Solving (PS)
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# circular perm

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CEO
Joined: 21 Jan 2007
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Kudos [?]: 854 [0], given: 4

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13 Mar 2008, 08:43
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6 guys (let's call them ABCDEF) sit around a circular table. If the AB must always sit together, and C must face the door, how many arrangements are possible? please explain your work...
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Kudos [?]: 3559 [0], given: 360

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13 Mar 2008, 09:19
48

1. "C must face the door" - the condition fixes circular shifts.
2. "the AB must always sit together" - we can consider AB one object, but count it twice as AB and BA .
3. We have 4 objects (3 guys and one couple ): 4P4=4!=24
4. finally, N=24*2=48
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Senior Manager
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13 Mar 2008, 10:32
48 it is

It looks like a circular permutation problem, but is a liner instead.
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20 Jan 2011, 08:49
Is it linear because the one guy must face the door?
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Re: circular perm   [#permalink] 20 Jan 2011, 08:49
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