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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
    ∴21st term = a + (21 - 1)d = a + 20d
    = 3 +20 × 6 = 123.


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