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    Question

    If the sum of n numbers in the GP 3, 6, 12, ... is 765

    then n is?
    A 12 Correct Answer Incorrect Answer
    B 6 Correct Answer Incorrect Answer
    C 8 Correct Answer Incorrect Answer
    D 4 Correct Answer Incorrect Answer

    Solution

    Given series is 3, 6, 12, ... Here, a = 3, r = 2 Sum of n numbers = Sn= 765 As we know that,┬аSum of n terms of GP = Sn┬а=┬аa(rn тАУ 1)/(r тАУ 1); where r >1 Sn┬а= 765 =┬а3┬а├Ч (2n┬атАУ 1) тЗТ 255 =┬а(2n тАУ 1) тЗТ 2n = 256 тЗТ 2n┬а= 28 тЗТ n = 8

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