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# A box contains 7 Yellow balls and 5 blue balls. Select 3

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Senior Manager
Joined: 25 Dec 2003
Posts: 360
Location: India
Followers: 1

Kudos [?]: 17 [0], given: 0

A box contains 7 Yellow balls and 5 blue balls. Select 3 [#permalink]  12 Jul 2004, 06:48
A box contains 7 Yellow balls and 5 blue balls. Select 3 balls randomly. What is the probability of choosing 3 blue ones.

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Giving another SHOT

Senior Manager
Joined: 05 Feb 2004
Posts: 290
Location: USA
Followers: 1

Kudos [?]: 3 [0], given: 0

3 balls can be chosen from 12 in : 12C3 ways
3 blue balls can be chosen from 5 blues in: 5C3 ways

Hence required prob: 5C3/12C3 = 10/220 = 1/22!!
Director
Joined: 04 Jul 2004
Posts: 905
Followers: 4

Kudos [?]: 25 [0], given: 0

Probability = (Fav. outcome) / (Total Outcome)

Total : selecting 3 balls from 12 balls = 12C3
Favourable : selecting 3 blue from 5 blue balls = 5C3

P = 5C3 / 12C3 (Very lengthy calculation)
Joined: 31 Dec 1969
Location: India
Concentration: General Management, Strategy
GMAT 1: 710 Q49 V0
GMAT 2: 740 Q40 V50
GMAT 3: 700 Q48 V38
GPA: 3.6
Followers: 0

Kudos [?]: 89 [0], given: 87156

I would do:

5/12 x 4/11 x 3/10 = 1/22 and forget about the combinations formula.
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