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# There are 5 identical Blue balls & 7 identical red

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Senior Manager
Joined: 21 Aug 2003
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There are 5 identical Blue balls & 7 identical red [#permalink]  25 Sep 2003, 05:13
There are 5 identical Blue balls & 7 identical red balls. Find the number of ways in which 2 balls can be selected.
SVP
Joined: 03 Feb 2003
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Since there are no restrictions on the taken balls, the answer should be 12C2.
Senior Manager
Joined: 21 Aug 2003
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caught in the trap...
try again.
Senior Manager
Joined: 21 Aug 2003
Posts: 258
Location: Bangalore
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Kudos [?]: 4 [0], given: 0

Does 12A2 means permutations..?
if yes, its wrong.
Manager
Joined: 02 Jul 2003
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This seems too easy to be right, but, sine you can't tell the balls a part besides the color red and blue

one blue and one red
one red and one bule
one red and one red
one blue and one blue

for a total of 4
Manager
Joined: 15 Sep 2003
Posts: 74
Location: california
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i would say 3 ways....assuming BR and RB are the same
Senior Manager
Joined: 21 Aug 2003
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thats correct. Answer is 3 ways.
We must remember that nCm is the number of ways m objects can be selected when there are n distinct objects. For identical objects we need to actually work it out.
Intern
Joined: 09 May 2004
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Location: houston, tx
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I was looking back on some old comb/perm problems, and had a question on this old post....

Why would the answer to this question be 3 instead of 4? If it is asking for the "number of ways" doesn't that indicate permutation, in which case order matters? Therefore, wouldn't we want to treat Blue/Red and Red/Blue as two distinct cases?

Therefore, four ways:
RR
BB
BR
RB

Can someone help? Thanks!
Intern
Joined: 29 Jun 2004
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gotta agree with guy 123 br and rb are the same thing..if the question hada stem askin us to pick the color r or b first or in some order then the answer wud have been different but it dont specify that.
Intern
Joined: 09 May 2004
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Location: houston, tx
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Ok... I see your point. Thanks!
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