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

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A box contains 7 Yellow balls and 5 blue balls. Select 3 [#permalink] New post 12 Jul 2004, 07:48
A box contains 7 Yellow balls and 5 blue balls. Select 3 balls randomly. What is the probability of choosing 3 blue ones.

explain steps please.
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 [#permalink] New post 12 Jul 2004, 08:45
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!!
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 [#permalink] New post 12 Jul 2004, 08:46
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)
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 [#permalink] New post 12 Jul 2004, 11:45
I would do:

5/12 x 4/11 x 3/10 = 1/22 and forget about the combinations formula.
  [#permalink] 12 Jul 2004, 11:45
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A box contains 7 Yellow balls and 5 blue balls. Select 3

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