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    Question

    The sum of the first 163 terms of a GP is equal to the

    sum of the first 161 terms in the same GP. If the 117th term in the same GP is 985, then what will be the sum of 150 terms?
    A 1 Correct Answer Incorrect Answer
    B 1.5 Correct Answer Incorrect Answer
    D 0.5 Correct Answer Incorrect Answer

    Solution

    According to the question,   if we take a(r163-1)/ r-1 =a(r161-1)/r-1 r163 = r161 r2 =1   r=±1   r = +1, the sum will be undefined. Taking r = -1, T117 = ar117-1 985 = a (-1)116 a=985 S150 =a(1-r")/1-r        (r 985(1-(-1)150)/1+1 985(1-1)/2=0 =0

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