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# One box contains 30 purple balls and 20 red balls, another

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Manager
Joined: 19 Aug 2006
Posts: 213

Kudos [?]: 72 [0], given: 0

One box contains 30 purple balls and 20 red balls, another [#permalink]

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08 Nov 2006, 16:39
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One box contains 30 purple balls and 20 red balls, another box contains 15 purple balls and 35 red balls, if Wendy randomly chooses one box and draws one ball from it, what will be the possibility that the ball will be purple?

Kudos [?]: 72 [0], given: 0

Senior Manager
Joined: 01 Sep 2006
Posts: 301

Kudos [?]: 28 [0], given: 0

Location: Phoenix, AZ, USA

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08 Nov 2006, 17:19
Prob fo selecting 1st box = 1/2 and prob to find puple in that 30/50
(1/2)*(3/5)=3/10
prob for slecting 2nd box 1/2 and prob to find purple 15/50

(1/2)*(15/50)= 3/20

combined 3/10+3/20=9/20

Kudos [?]: 28 [0], given: 0

GMAT Club Legend
Joined: 07 Jul 2004
Posts: 5034

Kudos [?]: 438 [0], given: 0

Location: Singapore

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08 Nov 2006, 18:10
Outcome can be purple from box1 OR purple from 2

Probability of picking eithe box = 1/2
Probability of picking purple from box1 = 30/50 * 1/2 = 3/10
Probability of picking purple form box2 = 15/50 * 1/2 = 3/20

Total = 3/10 + 3/20 = 9/20

(Easily understood if you drew a probability tree)

Kudos [?]: 438 [0], given: 0

Senior Manager
Joined: 05 Aug 2005
Posts: 409

Kudos [?]: 73 [0], given: 0

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08 Nov 2006, 21:18
9/20.......calculations as explained by other friends

Kudos [?]: 73 [0], given: 0

08 Nov 2006, 21:18
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