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Q: In a box, there are 9 blue, 6 white and some black stones. A stone is randomly selected and the probability that the stone is black is ¼. Find the total number of stones in the box?

  • 1
    15
  • 2
    18
  • 3
    20
  • 4
    24
  • Show Answer
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Answer : 3. "20"
Explanation :

Answer: C) 20 Explanation: We know that, Total probability = 1 Given probability of black stones = 1/4 => Probability of blue and white stones = 1 - 1/4 = 3/4 But, given blue + white stones =  9 + 6 = 15 Hence, 3/4 ----- 15  1   -----  ? => 15 x 4/3 = 20.   Hence, total number of stones in the box = 20.

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