Probability


  1. Two unbiased dice are thrown simultaneously. the probability of getting the sum divisible by 3, is ?









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    n(S) = 6 x 6 = 36
    n(E) = (1, 2) (2, 1), (1, 5) (2, 4) (3, 3) (4, 2) (5, 1) (3, 6) (4, 5) (5, 4) (6, 3) (6, 6) = 12

    Correct Option: B

    n(S) = 6 x 6 = 36
    n(E) = (1, 2) (2, 1), (1, 5) (2, 4) (3, 3) (4, 2) (5, 1) (3, 6) (4, 5) (5, 4) (6, 3) (6, 6) = 12
    ∴ P(E) = 12/36


  1. What is the possibility of getting at least 6 heads, if eight coins are tossed simultaneously ?









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    Required probability = Probability of getting 2 tails + Probability of getting 1 tail + Probability of getting no tail.

    Correct Option: A

    Required probability = Probability of getting 2 tails + Probability of getting 1 tail + Probability of getting no tail.
    = 8C2 x 1/256 + 8C1 x 1/256 + 8C0 x 1/256
    = 37/256



  1. A and B aim a target. The Probability that A hits the target is 5/7 and B hits the target in 7/10. What is the probability that exactly one of them hits the target ?









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    Required probability = P(A). P(B) + P (A ) . P(B)

    Correct Option: B

    Required probability = P(A). P(B) + P (A ) . P(B)
    = 5/7 . 3/10 + 2/7 . 7/10
    = 29/70


  1. A bag contains 5 white, 7 red and 8 black balls. If 4 balls are drawn one by one with replacement, what is the probability that all are white ?









  1. View Hint View Answer Discuss in Forum

    Probability that first ball drawn is white = 5C1 = 1/4
    Since, balls are drawn with replacement, hence all the four events will have equal probability.

    Correct Option: A

    Probability that first ball drawn is white = 5C1 = 1/4
    Since, balls are drawn with replacement, hence all the four events will have equal probability.
    Therefore, required probability = 1/4 x 1/4 x 1/4 x 1/4 = 1/256



  1. There are 8 blue and 4 white balls in a bag . A ball is drawn at random. Without replacing it another ball is drawn. Find the probability that both the balls drawn are blue ?









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    Total number of balls in the bag = 12
    Probability of drawing one blue ball in the first draw P(E1) = 8C1 / 12C1
    = 8/12 = 2/3

    After the first drawn of a blue ball, now there are 7 blue and 4 white ball in the bag. Total number of the balls in the bag is 11.

    Probability of drawing one blue ball in the second drawn = P(E2) = 7C1 /11C1 = 7/11

    Correct Option: B

    Total number of balls in the bag = 12
    Probability of drawing one blue ball in the first draw P(E1) = 8C1 / 12C1
    = 8/12 = 2/3

    After the first drawn of a blue ball, now there are 7 blue and 4 white ball in the bag. Total number of the balls in the bag is 11.

    Probability of drawing one blue ball in the second drawn = P(E2) = 7C1 /11C1 = 7/11

    ∴ Probability that both are blue P(E1 ∩ E2) = P(E1) x P(E2)
    = 2/3 x 7/11 = 14 / 33