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

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A box contains 6 black balls and 4 white balls. If two balls are selec  [#permalink]

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New post 18 Oct 2018, 00:41
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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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Re: A box contains 6 black balls and 4 white balls. If two balls are selec  [#permalink]

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New post 18 Oct 2018, 02:06
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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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Re: A box contains 6 black balls and 4 white balls. If two balls are selec  [#permalink]

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New post 18 Oct 2018, 02:57
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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New post 19 Oct 2018, 14:25
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.

Answer: C
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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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New post 22 Oct 2018, 01:53
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

Option C is the answer.
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Re: A box contains 6 black balls and 4 white balls. If two balls are selec   [#permalink] 22 Oct 2018, 01:53
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