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# In a jar, 9 balls are white and the rest are red. If two balls are to

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Math Expert
Joined: 02 Sep 2009
Posts: 52902
In a jar, 9 balls are white and the rest are red. If two balls are to  [#permalink]

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02 Oct 2018, 01:34
00:00

Difficulty:

35% (medium)

Question Stats:

81% (02:41) correct 19% (01:45) wrong based on 35 sessions

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In a jar, 9 balls are white and the rest are red. If two balls are to be chosen at random from the jar without replacement, the probability that the balls chosen will both be white is 6/11. What is the number of balls in the jar?

(A) 10
(B) 11
(C) 12
(D) 13
(E) 15

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Joined: 21 Nov 2016
Posts: 37
Re: In a jar, 9 balls are white and the rest are red. If two balls are to  [#permalink]

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02 Oct 2018, 02:44
1
The jar has 9 white balls, and the rest are red balls.
So, let total balls = t
The probability of picking 2 white balls without replacement is = 6/11
So, (9/t)x(8/t-1) = 6/11
on simplifying the above equation we would get a quadratic equation of the form,
t^2-t-132=0
Further simplifying we would get,
(t-12)(t+11)=0
Implies, t = 12, or t = -11
Since the no. of balls is supposed to be a positive integer, so t =12
So, the correct answer is C.
Re: In a jar, 9 balls are white and the rest are red. If two balls are to   [#permalink] 02 Oct 2018, 02:44
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