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MGMAT Guide 4 Word Translations p185 Chapter 12 4th edition

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woodenfootspa
 Post subject: MGMAT Guide 4 Word Translations p185 Chapter 12 4th edition
 Post Posted: Thu Aug 26, 2010 11:45 am 
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Course Students


Posts: 1
Hi!

I am having some problems with this example from the book

" Alicia Lives in a town whose streets are on a grid system with all the streets running E-W or N-S without breaks....."

(Forgive me for not typing out the whoel question as it was fairly lengthy)

Why is the total number of possibilities 6!/ (3!*3!)?
Shouldnt we be using the slot method (with 6 slots) as she can only choose between South and East at every turn? So...

2*2*2*2*2*2?

She doesnt have 6 choices at the 1st choice. Nor 5 at the 2nd....
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tim
 Post subject: Re: MGMAT Guide 4 Word Translations p185 Chapter 12 4th edition
 Post Posted: Mon Sep 20, 2010 7:11 pm 
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ManhattanGMAT Staff


Posts: 1779
Location: Southwest Airlines, seat 21C
She can't choose between E and S at every turn; if so, that would mean a path of EEEEEE or SSSSSS would work. The path she takes must include 3 Es and 3 Ss. So basically we have 6 steps, 3 of which must be E and 3 of which must be S. That's why you have to do 6!/(3!3!)..

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Tim Sanders
Manhattan GMAT Instructor
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