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Discussion :: Number Series

  1. In the series 3, 9, 15, ...... what will be the 21st term?

    2. A.

     117
    B.

     121
    C.

     123
    D.

     129

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    Answer : Option C

    Explanation :

    Clearly, 3 + 6 = 9, 9 + 6 = 15,.....
    So, the series is an A.P. in which a = 3 and d = 6.
    Therefore 21st term = a + (21 - 1) d = a + 20d = 3 + 20 x 6 = 123.

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