Combinatorics

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Combinatorics

by Giorgio » Wed Dec 16, 2009 12:19 pm
Six mobsters have arrived at the theater for the premiere of the film "Goodbuddies." One of the mobsters, Frankie, is an informer, and he's afraid that another member of his crew, Joey, is on to him. Frankie, wanting to keep Joey in his sights, insists upon standing behind Joey in line at the concession stand, though not necessarily right behind him. How many ways can the six arrange themselves in line such that Frankie's requirement is satisfied?

6

24

120

360

720

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OA is : d
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by Brent@GMATPrepNow » Wed Dec 16, 2009 12:44 pm
Giorgio wrote:Six mobsters have arrived at the theater for the premiere of the film "Goodbuddies." One of the mobsters, Frankie, is an informer, and he's afraid that another member of his crew, Joey, is on to him. Frankie, wanting to keep Joey in his sights, insists upon standing behind Joey in line at the concession stand, though not necessarily right behind him. How many ways can the six arrange themselves in line such that Frankie's requirement is satisfied?

6

24

120

360

720

This is from MGMAT,

OA is : d
Nice solution here: https://www.beatthegmat.com/probability-t22021.html
Brent Hanneson - Creator of GMATPrepNow.com
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by homersimpson » Fri Dec 18, 2009 2:03 pm
6 people can be arranged by 6! ways = 720 and half of the times Frankie will be behind Joey amd half od the times he will be ahead him so answer = 720/2 = 360

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by Giorgio » Fri Dec 18, 2009 2:11 pm
thanks!