Probability

  1. What is the probability that a number selected from the numbers 1, 2, 3, 4, 5....16 is a prime number ?
    1. 1/16
    2. 5/8
    3. 3/8
    4. 7/16
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    S = {1, 2, 3, ......16}
    E = {2, 3, 5, 7, 11, 13}
    ∴ P(E) = n(E)/n(S) = 6/16= 3/8

    Correct Option: C

    S = {1, 2, 3, ......16}
    E = {2, 3, 5, 7, 11, 13}
    ∴ P(E) = n(E)/n(S) = 6/16= 3/8

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  1. An urn contains 9 red, 7 white and 4 black balls. A ball is drawn at random. What is the probability that the ball drawn is not red ?
    1. 1/11
    2. 9/20
    3. 2/11
    4. 11/20
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    P (red) = 9 / (9 + 7 + 4) = 9/20

    Correct Option: D

    P (red) = 9 / (9 + 7 + 4) = 9/20
    ∴ P(not-red) = (1 - 9/20) = 11/20

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  1. In a lottery there are 20 prizes and 15 blanks. What is the probability of getting prize ?
    1. 1/10
    2. 2/5
    3. 4/7
    4. 2/7
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    P (getting a prize ) = 20 / (20 + 15 ) = 20 / 35 = 4/7

    Correct Option: C

    P (getting a prize ) = 20 / (20 + 15 ) = 20 / 35 = 4/7

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  1. The odds in favour of an event are 3 : 5. The probability of occurrence of the event is ?
    1. 3/5
    2. 3/8
    3. 1/3
    4. 1/5
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    Number of cases favourable of E = 3
    Total Number of cases = (3 + 5 ) = 8
    ∴ P(E) = 3/8

    Correct Option: B

    Number of cases favourable of E = 3
    Total Number of cases = (3 + 5 ) = 8
    ∴ P(E) = 3/8

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  1. The probability of getting heads in both trials when a balanced coin is tossed twice will be ?
    1. 1/4
    2. 1/2
    3. 1
    4. 3/4
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    Probability of getting head in one trail = 1/2
    ∴ Reqd Probability of getting heads in both the trails = 1/2 x 1/2 = 1/4

    Correct Option: A

    Probability of getting head in one trail = 1/2
    ∴ Reqd Probability of getting heads in both the trails = 1/2 x 1/2 = 1/4

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