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Posibility

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patrickgong6688
 Post subject: Posibility
 Post Posted: Fri Jul 08, 2011 12:02 pm 
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Posts: 10
A first grade teacher use ten flash cards,numbered 1 through 10 ,to teach her students to order numbers correctly.She has students choose four flash cards randomly,then arrange the cards in ascending order.One day,she removes the cards numbered 2 and 4 from the deck of flash cards.On that day,how many different correct arrangements of four randomly selected cards are possible?
A70 B210 C336 D840 E1680
Anwser is A Can someone give me a reply ?
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george.kourdin
 Post subject: Re: Posibility
 Post Posted: Mon Jul 11, 2011 11:07 am 
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Course Students


Posts: 98
assuming that the problem does not care about consecutive oder - i.e. a correct arrangement does not have to be consecutive integers and can contain gaps, think its like this

start with 10 cards
remove 2 (doesn't matter which, the actual numbers are irrelevant here). we now have 8 total cards.

a student is a choosing 4 cards out of a population of 8 cards.
n!/k!(n-k)! = 8!/(4!*4!) = 70
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jnelson0612
 Post subject: Re: Posibility
 Post Posted: Thu Jul 14, 2011 12:05 pm 
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ManhattanGMAT Staff


Posts: 1857
Thanks George!

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Jamie Nelson
ManhattanGMAT Instructor
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