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If a bag contains only red and blue balls and probability of picking

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Math Expert
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Joined: 02 Aug 2009
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If a bag contains only red and blue balls and probability of picking  [#permalink]

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New post 25 Jan 2018, 21:18
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If a bag contains only red and blue balls and probability of picking red ball is 1/2, how many red balls are there in bag?

(1) If 10 blue balls are removed from the bag, the probability of picking red ball becomes 3/5.
(2) The number of red balls are 30 less than the total number of balls in the bag.

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Re: If a bag contains only red and blue balls and probability of picking  [#permalink]

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New post 25 Jan 2018, 22:47
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chetan2u wrote:
If a bag contains only red and blue balls and probability of picking red ball is 1/2, how many red balls are there in bag?

(1) If 10 blue balls are removed from the bag, the probability of picking red ball becomes 3/5.
(2) The number of red balls are 30 less than the total number of balls in the bag.

New question
source - self


Let total number of balls in the bag = x. Given that probability of picking red ball = 1/2, it means x/2 balls are red and remaining x/2 are blue.

(1) If we remove 10 blue balls, total balls left = x-10, and red balls are still = x/2.
The probability of picking a red ball now = (x/2) / (x-10) ; which is given as 3/5. Solving this we get x=60.
So number of red balls = x/2 = 30. Sufficient.

(2) Total balls - red balls = x - x/2 = 30 (given)
Solving this we get x=60. Thus the number of red balls = 30. Sufficient.

Hence D answer
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Re: If a bag contains only red and blue balls and probability of picking  [#permalink]

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New post 02 Jul 2019, 07:33
Nice question. Since there are only reds and blues then that means that probabilities are split 50:50, and thus they should be of equal quantities. D1: provides an exact quantity which +/- and resulting change to probability which should give us the final number D2: Only one number can be 30 less than the total, equaling to the rest of the amount of balls.
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Re: If a bag contains only red and blue balls and probability of picking   [#permalink] 02 Jul 2019, 07:33
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If a bag contains only red and blue balls and probability of picking

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