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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: 222
Followers: 1

Kudos [?]: 16 [0], given: 0

One box contains 30 purple balls and 20 red balls, another [#permalink]  08 Nov 2006, 15:39
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Question Stats:

0% (00:00) correct 0% (00:00) wrong based on 0 sessions
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?
Senior Manager
Joined: 01 Sep 2006
Posts: 301
Location: Phoenix, AZ, USA
Followers: 1

Kudos [?]: 15 [0], given: 0

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
GMAT Club Legend
Joined: 07 Jul 2004
Posts: 5068
Location: Singapore
Followers: 23

Kudos [?]: 195 [0], given: 0

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)
Senior Manager
Joined: 05 Aug 2005
Posts: 413
Followers: 1

Kudos [?]: 15 [0], given: 0

9/20.......calculations as explained by other friends
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