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# GMAT prep II - probability question

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Intern
Joined: 06 Oct 2007
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GMAT prep II - probability question [#permalink]  26 Nov 2007, 13:40
Hi!
This is a pretty basic one, but I got it wrong...

Josh and Jose work at an auto repair center with 4 other workers. For a survey on health insurance, 2 of the 6 workers will be randomly chosen to be interviewed. What is the probability that both Josh and Jose will be chosen?

a) 1/15
b) 1/12
c) 1/9
d) 1/6
e) 1/3

Thanks!
-Jackie
CEO
Joined: 17 Nov 2007
Posts: 3578
Concentration: Entrepreneurship, Other
Schools: Chicago (Booth) - Class of 2011
GMAT 1: 750 Q50 V40
Followers: 406

Kudos [?]: 2140 [0], given: 359

Expert's post
A

P=1/c(2,6)=4!*2!/6!=2/30=1/15

another way:

P=1/6*1/5+1/6*1/5=1/15
CEO
Joined: 29 Mar 2007
Posts: 2591
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Kudos [?]: 234 [0], given: 0

Re: GMAT prep II - probability question [#permalink]  26 Nov 2007, 16:34
jthong wrote:
Hi!
This is a pretty basic one, but I got it wrong...

Josh and Jose work at an auto repair center with 4 other workers. For a survey on health insurance, 2 of the 6 workers will be randomly chosen to be interviewed. What is the probability that both Josh and Jose will be chosen?

a) 1/15
b) 1/12
c) 1/9
d) 1/6
e) 1/3

Thanks!
-Jackie

Oops messed it up a bit.

A.

6!/4! = 30. We have J and J and then J and J. so 2/30= 1/15.
SVP
Joined: 28 Dec 2005
Posts: 1583
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Kudos [?]: 88 [0], given: 2

why do we have to consider two cases, and not just have the probability as 1/6*1/5 ?
CEO
Joined: 17 Nov 2007
Posts: 3578
Concentration: Entrepreneurship, Other
Schools: Chicago (Booth) - Class of 2011
GMAT 1: 750 Q50 V40
Followers: 406

Kudos [?]: 2140 [0], given: 359

Expert's post
pmenon wrote:
why do we have to consider two cases, and not just have the probability as 1/6*1/5 ?

we have two cases: (Josh,Jose) and (Jose,Josh)

for (Josh,Jose): 1/6*1/5 and for (Jose,Josh): 1/6*1/5
Manager
Joined: 03 Sep 2006
Posts: 233
Followers: 1

Kudos [?]: 5 [0], given: 0

Late, but A:
2C2 / 6C2
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