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A box contains 6 black balls and 4 white balls. If two balls are selec

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Math Expert
Joined: 02 Sep 2009
Posts: 59020
A box contains 6 black balls and 4 white balls. If two balls are selec  [#permalink]

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18 Oct 2018, 01:41
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Difficulty:

5% (low)

Question Stats:

84% (01:00) correct 16% (01:02) wrong based on 90 sessions

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A box contains 6 black balls and 4 white balls. If two balls are selected at random without replacement, what is the probability that both balls are white?

A. 7/90
B. 3/25
C. 2/15
D. 4/25
E. 4/9

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Joined: 17 Dec 2016
Posts: 19
Location: Viet Nam
Re: A box contains 6 black balls and 4 white balls. If two balls are selec  [#permalink]

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18 Oct 2018, 03:06
1
Bunuel wrote:
A box contains 6 black balls and 4 white balls. If two balls are selected at random without replacement, what is the probability that both balls are white?

A. 7/90
B. 3/25
C. 2/15
D. 4/25
E. 4/9

The probability of both balls are white = 2C4/ 2C10 = 2/15

Hence, choice C is the answer
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Joined: 22 Feb 2018
Posts: 415
Re: A box contains 6 black balls and 4 white balls. If two balls are selec  [#permalink]

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18 Oct 2018, 03:57
OA:C

Probability that both ball are white$$= \frac{C(4,2)}{C(10,2)}= \frac{4!}{2!2!}*\frac{2!8!}{10!}=\frac{4*3}{2*1}*\frac{2*1}{10*9}=\frac{2}{15}$$
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Re: A box contains 6 black balls and 4 white balls. If two balls are selec  [#permalink]

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19 Oct 2018, 15:25
Bunuel wrote:
A box contains 6 black balls and 4 white balls. If two balls are selected at random without replacement, what is the probability that both balls are white?

A. 7/90
B. 3/25
C. 2/15
D. 4/25
E. 4/9

There are 10 balls in the box. The probability that the first ball drawn will be white is 4/10, and the probability that the second ball will also be white is 3/9. Thus, the probability of selecting two white balls, without replacement, is 4/10 x 3/9 = 2/5 x 1/3 = 2/15.

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Joined: 25 Apr 2018
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Re: A box contains 6 black balls and 4 white balls. If two balls are selec  [#permalink]

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22 Oct 2018, 02:53
Bunuel wrote:
A box contains 6 black balls and 4 white balls. If two balls are selected at random without replacement, what is the probability that both balls are white?

A. 7/90
B. 3/25
C. 2/15
D. 4/25
E. 4/9

Ways of selecting 2 white balls = 4C2
probability of selecting 2 white balls= 4C2/10C2 =2/15

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Re: A box contains 6 black balls and 4 white balls. If two balls are selec   [#permalink] 22 Oct 2018, 02:53
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