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25 Jan 2018, 21:18
Kudos
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D
Be sure to select an answer first to save it in the Error Log before revealing the correct answer (OA)!
Difficulty:
35%
(medium)
Question Stats:
69% (01:34) correct
31%
(01:58)
wrong
based on 200
sessions
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Not Attempted Yet
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
(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
25 Jan 2018, 22:47
Kudos
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chetan2u
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
02 Jul 2019, 07:33
Kudos
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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.
