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    Question

    In a tank, the ratio of petrol to kerosene is 7:5. 50% of

    this mixture is removed and replaced with kerosene. Again, 50% is replaced with petrol. Find the final ratio of petrol to kerosene in the tank.
    A 20:19 Correct Answer Incorrect Answer
    B 16:17 Correct Answer Incorrect Answer
    C 31:17 Correct Answer Incorrect Answer
    D 21:24 Correct Answer Incorrect Answer

    Solution

    ATQ,


    Petrol = 7x, Kerosene = 5x → Total = 12x litres

    First step (50% replaced with kerosene):

    Petrol = 0.5 × 7x = 3.5x litres

    Kerosene = 0.5 × 5x + 0.5 × 12x = 2.5x + 6x = 8.5x litres

    Second step (50% replaced with petrol):

    Petrol = 0.5 × 3.5x + 0.5 × 12x = 1.75x + 6x = 7.75x litres

    Kerosene = 0.5 × 8.5x = 4.25x litres

    Final ratio = 7.75x : 4.25x = 775 : 425 = 31:17

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