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    The mean of the first eight odd natural numbers is:
    Question

    The mean of the first eight odd natural numbers is:

    A.

    9

    B.

    11

    C.

    8

    D.

    10

    Correct option is C

    Given:

    First eight odd natural numbers.

    Formula Used :

    Sum of the first n terms of an AP:

    Sn=n2[2a+(n1)d]S_n = \frac{n}{2}[2a + (n-1)d]​​

    Solution:

    The first eight odd natural numbers are: 1, 3, 5, 7, 9, 11, 13, and 15.

    Here, n = 8, a = 1, and d = 2.

    S8=82[2(1)+(81)(2)]S_8 = \frac{8}{2}[2(1) + (8-1)(2)]​​

    S8=4[2+7(2)]S_8 = 4[2 + 7(2)]​​

    S8=4[2+14]S_8 = 4[2 + 14]​​

    S8=4[16]S_8 = 4[16]​​

    S8=64S_8 = 64​​

    Mean = S88=648=8\frac{S_8}{8} = \frac{64}{8} = 8​​

    Therefore, the mean of the first eight odd natural numbers is 8.

    Alternate Method:

    For the first n odd natural numbers, the sum is n2.n^2.​​

    In this case, we have the first 8 odd natural numbers, so their sum is 82=64.8^2 = 64.​​

    The mean is then the sum divided by the number of terms:648=8. \frac{64}{8} = 8.​​

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