Probability


  1. A box contains 3 white and 2 red balls. If we draw one ball and ball and without replacing the first ball. The probability of drawing red ball in the second drawn is ?









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    Total balls in the box = 5
    Second red ball can be drawn in two ways
    Case I. First ball is white and second ball is red.
    Its probability = 3/5.2/4 = 6/20 = 3/10
    Case II: First ball is red and second ball is red
    Its probability = 2/5.1/4 = 2/20 = 1/10

    Correct Option: B

    Total balls in the box = 5
    Second red ball can be drawn in two ways
    Case I. First ball is white and second ball is red.
    Its probability = 3/5.2/4 = 6/20 = 3/10
    Case II: First ball is red and second ball is red
    Its probability = 2/5.1/4 = 2/20 = 1/10
    Hence, reqd. probability
    = 3/10 + 1/10 = 4/10 = 2/5


  1. Three mangoes and three apples are kept in a box. if two fruits are chosen at random. find the probability that one is a mango and the other is an apple.











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    Total number of ways
    = n(s) = 6c2 = 15
    Favorable number of ways
    = n(E) = 3C1 x 3C1= 9

    Correct Option: B

    Total number of ways
    = n(s) = 6c2 = 15
    Favorable number of ways
    = n(E) = 3C1 x 3C1= 9
    ∴ Required probability = 9/15 = 3/5



  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. 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. 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