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# A box contains exactly 22 balls, of which 11 are white and 11 are blac

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Math Expert
Joined: 02 Sep 2009
Posts: 58410
A box contains exactly 22 balls, of which 11 are white and 11 are blac  [#permalink]

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02 Oct 2018, 02:18
00:00

Difficulty:

5% (low)

Question Stats:

93% (01:12) correct 7% (01:53) wrong based on 55 sessions

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A box contains exactly 22 balls, of which 11 are white and 11 are black. If two balls are to be picked from this box at random and without replacement, what is the probability that both balls will be black?

(A) 1/6

(B) 5/21

(C) 5/11

(D) 11/40

(E) 17/40

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Joined: 19 Oct 2013
Posts: 516
Location: Kuwait
GPA: 3.2
WE: Engineering (Real Estate)
Re: A box contains exactly 22 balls, of which 11 are white and 11 are blac  [#permalink]

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03 Oct 2018, 14:52
Bunuel wrote:
A box contains exactly 22 balls, of which 11 are white and 11 are black. If two balls are to be picked from this box at random and without replacement, what is the probability that both balls will be black?

(A) 1/6

(B) 5/21

(C) 5/11

(D) 11/40

(E) 17/40

Keyword: without replacement

Total possibilities = 22
Total black = 11

Probability 2 black balls = 11/22 * 10/21 = 1/2 * 10/21 = 5/21

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Re: A box contains exactly 22 balls, of which 11 are white and 11 are blac  [#permalink]

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04 Oct 2018, 19:32
Bunuel wrote:
A box contains exactly 22 balls, of which 11 are white and 11 are black. If two balls are to be picked from this box at random and without replacement, what is the probability that both balls will be black?

(A) 1/6

(B) 5/21

(C) 5/11

(D) 11/40

(E) 17/40

The probability of selecting two black balls is 11/22 x 10/21 = 1/2 x 10/21 = 5/21.

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Re: A box contains exactly 22 balls, of which 11 are white and 11 are blac   [#permalink] 04 Oct 2018, 19:32
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