Probability Practice Questions: Level 02

  1. What is the probability of getting at least one 3 in 2 throws of a dice?
    1. 1/36
    2. 5/36
    3. 11/36
    4. 35/36
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    Sol : Option 3
    Total possible outcomes = 36.
    Favorable cases = 11 i.e. (3, 1) (3, 2) (3, 3) (3, 4) (3, 5) (3, 6). (1, 3) (2, 3) (4, 3) ,(5, 3) ,(6, 3)
    Therefore, Reqd. Probability = 11 / 36
  2. The probability of A’s winning a game of chess against B is 2/3. What is the probability that A will win at least 1 of a total of two games?
    1. 1/27
    2. 19/27
    3. 2/27
    4. 8/9
    Sol : Option 4
    Reqd. Probability = 1 – (A not winning even one Game out of 3) =1 - (1/3)2 = 1 - (1/9) = (8/9)
  3. What is the probability that a non-leap year will have 53 Mondays?
    1. 52/53
    2. 51/52
    3. 1
    4. None of these
    Sol : Option 4
    Non Leap Year = 52 Weeks and one Day.
    Prob. of one days Day being Monday = 1 / 7
    Therefore, Reqd. Prob. = 1 / 7
Directions for questions 4 to 6: Read the following information and answer the questions that follow. The probability that A will pass the examination is 1/2 and the probability that B will pass the examination is 1/3.
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  1. What is the probability that both A and B will pass the examination?
    1. 1/6
    2. 1
    3. 2/3
    4. 1/3
    Sol : Option 1
    Probability that A will pass in exam = 1/2
    So, Probability that A will fail in exam = 1/2.
    Probability that B will pass in exam = 1/3
    So, Probability that B will fail in exam = 2/3.
    Probability that both will pass in the exam = Probability that A will pass and probability that B will pass
    = 1/2 x 1/3 = 1/6
  2. What is the probability that only 1 person [either A or B] will pass the examination?
    1. 1
    2. 1/2
    3. 1/3
    4. 2/3
    Sol : Option 2
    Probability that only one person will pass is when A passes and B fails or A fails and B passes.
    = (1/2) x (2/3) + (1/2) x (1/3) = 1/2
  1. What is the probability that at least one person will pass the examination?
    1. 1
    2. 1/2
    3. 1/3
    4. 2/3
    Sol : Option 4
    Probability that at least one person, will pass, so the possibilities
    can be (A pass and B fails), or (A fails and B pass) or (Both A and B pass)
    (1/2) x (2/3) + (1/2) x (1/3) + (1/2) x (1/3) = 2/3
  2. Three cards are drawn together from a pack of 52 cards at random. What is the probability that all the cards are Diamonds?
    1. 4C3 / 2C3
    2. 13C3 / 52C3
    3. 26C3 / 52C3
    4. 8C3 / 52C3
    Sol : Option 2
    There are 13 diamonds. Three diamonds out of 13 diamonds can be taken out in 13C3 ways.
    Total number of sample spaces = 52C3
    Required probability = 13C3 / 52C3
  3. A bag contains 8 blue balls and 6 black balls. Three balls are drawn one by one with replacement. What is the probability that all the 3 balls are black?
    1. 27 / 343
    2. 1 / 343
    3. 18 / 343
    4. None of these
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    Sol : Option 1
    P (of black ball in first attempt) = 6 / 14 = 3 / 7
    Here probability will remain same for the next two attempt.
    Therefore, Required Probability = (3/7) x (3/7) x (3/7) = 27 / 343
  4. One bag contains 8 blue balls and 6 Green balls; another bag contains 7 blue balls and 5 green balls. If one ball is drawn from each bag, determine the probability that both are blue?
    1. 1/2
    2. 1/3
    3. 1/4
    4. 1/5
    Sol : Option 2
    Bag I Bag II
    8 blue 7 blue
    6 green 5 green
    Probability of getting blue ball from bag I = 8 / 14
    Probability of getting blue ball from bag II = 7 / 12
    Hence reqd. Prob. = (8/14) x (7/12) = (1/3)
  5. 1 ball is drawn at random from a box containing 4 red balls, 5 white balls and 6 blue balls, what is the probability that the ball is a red ball?
    1. 1/7
    2. 2/15
    3. 4/15
    4. 1/15
    Sol : Option 3
    Total possible outcomes = 15. (i.e. One out of 15 balls).
    Favorable outcomes (one out of 4 red balls) = 4.
    Reqd. Probability = 4 / 15
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