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    Question

    Two trains, A and B, cross each other in 20 seconds and

    30 seconds respectively, when running in opposite and the same direction respectively. If the speed of the slower trains is n% of the speed of the faster trains, then find the value of (n × 2).
    A 40 Correct Answer Incorrect Answer
    B 50 Correct Answer Incorrect Answer
    C 75 Correct Answer Incorrect Answer
    D 80 Correct Answer Incorrect Answer
    E None of these Correct Answer Incorrect Answer

    Solution

    Let the speed of train A be S1 and the speed of train B be S2. And length of train A be L1 and the length of train B be L2. According to the question, (S1 + S2) = (L1 + LB)/20 And, (S1 - S2) = (L1 + LB)/30 Here, the length of both the train is equal. So, (S1 + S2) × 20 = (S1 - S2) × 30 => 20 S1 + 20 S2 = 30 S1 – 30 S2 => 10 S1 = 50 S2 => S1/S2 = 50/10 = 5/1 Speed of slower train = n% of faster train => n% = (1/5) × 100 = 20% Therefore, (n × 2) = 20 × 2 = 40

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