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

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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, 20:18
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Question Stats:

70% (01:34) correct 30% (01:26) wrong based on 61 sessions

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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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1) Absolute modulus : http://gmatclub.com/forum/absolute-modulus-a-better-understanding-210849.html#p1622372
2)Combination of similar and dissimilar things : http://gmatclub.com/forum/topic215915.html
3) effects of arithmetic operations : https://gmatclub.com/forum/effects-of-arithmetic-operations-on-fractions-269413.html


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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, 21:47
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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
GMAT Club Bot
Re: If a bag contains only red and blue balls and probability of picking &nbs [#permalink] 25 Jan 2018, 21:47
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If a bag contains only red and blue balls and probability of picking

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