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Home Aptitude Probability See What Others Are Saying!
  • Question
  • A speaks truth in 60% of the cases and B in 80% of the cases. In what percentage of cases are they likely to contradict each other, narrating the same incident?


  • Options
  • A. 70%
  • B. 36%
  • C. 22%
  • D. 44%

  • Correct Answer
  • 44% 

    Explanation

    Let A = Event that A speaks the truth
    and B = Event that B speaks the truth
    Then, P(A) = 60/100 = 3/5 and P(A) = 80/100 = 4/5
    ? P(A) = (1 - 3/5) = 2/5 and
    P(B) = (1 - 4/5) = 1/5

    P(A and B contradict each other)
    = P [(A speaks the truth and B tells a lie) or (A tells a lie and B speak the truth)]
    =P[(A and B) or (A and B)]
    =P(A and B) + P (A and B)
    = P(A) x P(B) + P(A) x P(B)
    = (3/5 x 1/5) + ( 2/5 x 4/5)
    = (3/25 + 8/25 ) = 11/25
    = (11/25 x 100)% = 44%


  • More questions

    • 1. 
      The ratio of length and breadth of a rectangle is 5 : 3 .If length is 8 m more than breadth, find the area of the rectangle.

    • Options
    • A. 300 sq m
    • B. 250 sq m
    • C. 240 sq m
    • D. 185 sq m
    • Discuss
    • 2. 
      What rate percent does a man get for his money when in discounting a bill due 10 months hence he deducts 4% of the amount of the bill?

    • Options
    • A. 5%
    • B. 6%
    • C. 8%
    • D. 4%
    • Discuss
    • 3. 
      The face value of a bill due 5 yr hence is ? 13800. If the rate of simple interest is 5% per annum, what will be the banker's gain at the bill?

    • Options
    • A. ? 690
    • B. ? 600
    • C. ? 590
    • D. ? 625
    • Discuss
    • 4. 
      The true discount on a bill 24 months, hence at 24% per annum, is ? 144. What will be the banker's discount?

    • Options
    • A. ? 213.12
    • B. ? 415
    • C. ? 515.12
    • D. ? 616
    • Discuss
    • 5. 
      In a game of 160 points, A can give 10 points to B and 30 points to C. How many points B can give C in a game of 60?

    • Options
    • A. 10
    • B. 15
    • C. 6
    • D. 8
    • Discuss
    • 6. 
      The true discount on a bill for Rs. 2520 due 6 months hence at 10 % per annum is :

    • Options
    • A. Rs. 180
    • B. Rs. 140
    • C. Rs. 80
    • D. Rs. 120
    • Discuss
    • 7. 
      In 1 km race, P beats Q by 72 m in 12 s. Find the P's time over the course.

    • Options
    • A. 1552/3 s
    • B. 151 s
    • C. 1542/3 s
    • D. 160 s
    • Discuss
    • 8. 
      The banker's gain of a certain sum due 2 years hence at 10% per annum is Rs. 24. What is the present worth?

    • Options
    • A. Rs. 600
    • B. Rs. 500
    • C. Rs. 400
    • D. Rs. 300
    • Discuss
    • 9. 
      The banker's gain on a bill due 1 year hence at 5% is Re. 1. The true discount is?

    • Options
    • A. ? 15
    • B. ? 20
    • C. ? 25
    • D. ? 5
    • Discuss
    • 10. 
      The true discount on a bill of Rs. 1860 due after 8 months is Rs. 60. Find the banker's gain?

    • Options
    • A. Rs. 1.5
    • B. Rs. 2.5
    • C. Rs. 4
    • D. Rs. 2
    • Discuss


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