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    Question

    If x + y = 4 and (1/x) + (1/y) = 24/7, then the value of

    (x3 + y3).
    A 40 Correct Answer Incorrect Answer
    B 100 Correct Answer Incorrect Answer
    C 90 Correct Answer Incorrect Answer
    D 50 Correct Answer Incorrect Answer

    Solution

    Since, (1/x) + (1/y) = 24/7 So, (x + y)/xy = 24/7 Or, xy = (4 × 7)/24 = 7/6 (x + y)3 = x3 + 3xy(x + y) + y3 So, x3 + y3 = 43 – 3 × 4 × (7/6) = 64 – 14 = 50  

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