New Enroll in RBI Grade B New Batch - Starts on May 21

    Question

    Two candles of the same height are lighted at the same

    time. The first is consumed in 10 hours and the second in 8 hours. Assuming that each candle burns at a constant rate, in how many hours after being lighted, the ratio between first and second candles becomes 4:1.
    A 5 hours 30 minutes Correct Answer Incorrect Answer
    B 7 hours 30 minutes Correct Answer Incorrect Answer
    C 8 hours 10 minutes Correct Answer Incorrect Answer
    D 6 hours 30 minutes Correct Answer Incorrect Answer
    E None of these Correct Answer Incorrect Answer

    Solution

    Let the candle height is 1 meter. Let the required time =‘t’ hours In 10 hours first candle lighted = 1 So in 1 hour first candle lighted = t/10 After ‘t’ hours remaining first candle = (1 - t/10) Similarly, After ‘t’ hours remaining second candle = (1 - t/8) So the ratio between the first and second candle after being lighting = ((1 - t/10))/((1 - t/8)) = 4/1 1 - t/10 = 4 - (4t)/8 t/2 - t/10 = 4 – 1 (5t - t)/10 = 3 T = 15/2 hours or 7 hours 30 minutes

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