Probability


  1. Out of 13 applicants for a job, there are 5 women and 8 men It is desired to select 2 persons for the job, The probability that atleast one of the selected persons will be a woman, is











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    Total ways = 13c2
    Favourable number ways of selecting men only = 8c2
    ∴ Probability of selecting no woman
    = 8c2 / 13c2
    = 14/39

    Correct Option: A

    Total ways = 13c2
    Favourable number ways of selecting men only = 8c2
    ∴ Probability of selecting no woman
    = 8c2 / 13c2
    = 14/39
    ∴ Probability of selecting at least one woman
    = 1 - (14 / 39)
    = 25 / 39


  1. Five coins are tossed at a time. Then, the probability of obtaining at least one tail is











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    Total events = n (s) = 25 = 32
    n(E) of getting heads = 1
    p(E) = 1/32
    ∴ n(E) = 1 - p(E)

    Correct Option: A

    Total events = n (s) = 25 = 32
    n(E) of getting heads = 1
    p(E) = 1/32
    ∴ n(E) = 1 - p(E) = 1 - 1/32 = 31/32



  1. A and B are two events such that P(A) = 0.3 and P ( A∪B) = 0.8. If A and B are independent, then P (B) is











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    Let P(B) = x
    Given, P(A∪B) = 0.8 and P(A) = 0.3
    ⇒ P(A) + P(B) - P(A∩B) = 0.8
    ⇒ P(A) + P(B) - P(A) P(B) = 0.8 {∵A and B are independent}

    Correct Option: E

    Let P(B) = x
    Given, P(A∪B) = 0.8 and P(A) = 0.3
    ⇒ P(A) + P(B) - P(A∩B) = 0.8
    ⇒ P(A) + P(B) - P(A) P(B) = 0.8 {∵A and B are independent}
    ⇒ 0.3 + x - 0.3x = 0.8
    ⇒ 0.7x = 0.5
    ∴ x = 5/7


  1. A box contains 24 marbles, some are green and other are blue. If a marble is drawn at random from the box, the porbability that it is green is 2/3. The number of blue balls in the box is









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    Let the number of green marble = x
    Then, Probability of getting a green marble
    = xc1 / 24c1 = 2/3

    Correct Option: D

    Let the number of green marble = x
    Then, Probability of getting a green marble
    = xc1 / 24c1 = 2/3
    ⇒ x/24 = 2/3
    ⇒ x = 16



  1. A bag contains 3 red, 4 white and 7 black balls. The probability of drawing a red or a black ball, is











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    Here, total balls are 14.
    ∴ Required probability = (3c1 + 7c1) / 14c1

    Correct Option: C

    Here, total balls are 14.
    ∴ Required probability = (3c1 + 7c1) / 14c1
    = (3 + 7)/14
    = 10/14
    = 5/7