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    Question

    Find the sum of 4 terms of the geometric series - 21,

    42, 84,
    A 325 Correct Answer Incorrect Answer
    B 320 Correct Answer Incorrect Answer
    C 315 Correct Answer Incorrect Answer
    D 327 Correct Answer Incorrect Answer

    Solution

    4 terms of the product series 21, 42, 84, 168   Sum = 21 + 42 +84 + 168 = 21 (1+2+4+8)   21x1 5=315. IInd Method: a=21, r=42/21=2, n=4 Sn=a(rn-1)/r-1 21(24-1)/ 2-1 (21×15)/1 =315.

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