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# Signal flags

Author Message
Director
Joined: 01 Apr 2008
Posts: 821
Name: Ronak Amin
Schools: IIM Lucknow (IPMX) - Class of 2014

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22 Mar 2009, 21:50
Each signal that a certain ship can make is comprised of 3 different flags hanging
vertically in a particular order. How many unique signals can be made by using 4
different flags?
A. 10
B. 12
C. 20
D. 24
E. 36

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Manager
Joined: 02 Jul 2007
Posts: 111

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23 Mar 2009, 11:56
I get D(24)

there are 6 ways to uniquely order 3 different flags (also, 3!)
1 1 2 2 3 3
2 3 3 1 1 2
3 2 1 3 2 1

there are 4 ways to put 4 flags in 3 different groups (also 4C3 ---> n!/r!(n-r)!)
1 1 2 3
2 2 3 4
3 4 4 1

6x4=24
CEO
Joined: 17 Nov 2007
Posts: 3484
Concentration: Entrepreneurship, Other
Schools: Chicago (Booth) - Class of 2011
GMAT 1: 750 Q50 V40

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23 Mar 2009, 15:41
or $$P^4_3 = 24$$

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Re: Signal flags &nbs [#permalink] 23 Mar 2009, 15:41
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# Signal flags

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