2009 November 1st, 04:48 PM
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#1 (permalink) |
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GMAT: 740(M50, V40)
 
Join Date: Feb 2009
Posts: 400
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probability
A bag contains 7 white and 9 black balls. if 2 balls drawn at random, what are the chances of 1 white and 1 black?
(7C1 * 9C1) / 16C2 OR 2*(7C1 * 9C1) / 16C2
_ _ _ _ SIG _ _ _ _
730+...this time or never!! |
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2009 November 2nd, 01:26 AM
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#2 (permalink) | |
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Online GMAT/GRE tutor
Join Date: Sep 2009
Location: Halfmoon Bay, BC, Canada
Posts: 34
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Quote:
P(1 black and 1 white) = P(1st ball is black & 2nd is white OR 1st ball is white & 2nd is black) = P(1st ball is black & 2nd is white) + P(1st ball is white & 2nd is black) = (9/16 x 7/15) + (7/16 x 9/15) = 126/240 = 21/40 |
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