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    Question

    Train P and train Q start from the same point on

    parallel tracks with speeds of 8 km/hr and 16 km/hr respectively. After 2 hours, train P doubles its speed, and train Q reduces its speed by 50%. They then reach the destination together. Find the total time taken from the start.
    A 2 hrs Correct Answer Incorrect Answer
    B 4 hrs Correct Answer Incorrect Answer
    C 7 hrs Correct Answer Incorrect Answer
    D 10 hrs Correct Answer Incorrect Answer
    E None of these Correct Answer Incorrect Answer

    Solution

    ATQ, Distance travelled in first 2 hours: Train P = 8 × 2 = 16 km Train Q = 16 × 2 = 32 km New speeds: Train P = 8 × (200/100) = 16 km/hr Train Q = 16 × (50/100) = 8 km/hr Gap between them after 2 hours = 32 – 16 = 16 km Now Train P is faster; relative speed = 16 – 8 = 8 km/hr Time taken to cover the gap = 16 / 8 = 2 hours Total time taken = 2 + 2 = 4 hours

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