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Deepak Bora
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The probability of selecting a blue marble at random from a jar that contains only blue, black and green marbles is 1/5 . The probability of selecting a black marble at random from the same jar is 1/4 . If the jar contains 11 green marbles, find the total number of marbles in the jar.

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CBSE 10th Class past year question paper

Year 2019

SET 1, Code Number- 30/2/1

Question number – 9

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1 Answer

  1. This answer was edited.

    P(blue marble) = 1/5
    P(black marble) = 1/4
    ∴ P(green marble) = 1 – ( (1/5) + (1/4))

    = 11/20
    Let total number of marbles be X
    then,

    (11/20) × X = 11

    X = 20

     

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