The mean of the five observations x, x + 2, x + 4, x + 6, x + 8 is 11.

The mean of the five observations x, x + 2, x + 4, x + 6, x + 8 is 11. Then the mean of the first three observations is
(a) 12
(b) 2
(c) 20
(d) 9

Anurag Mishra Professor Asked on 23rd February 2016 in Maths.
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    Best answer

    Answer: (d) 9 

    Solution:-
    The mean of five observation x, x + 2, x + 4, x + 6, x + 8 is 11.
    Then, (x + x + 2 + x + 4 + x + 6 + x + 8)/5 = 11
    (5 x + 20) = 11 x 5
    5 x = 55 – 20
    5 x = 35
    x = 35/5
    x =  7

    Then, the value of first three observations x = 7, x + 2 = 7 + 2 = 9, x + 4 = 7 + 4= 11
    So, mean of first three observations = (7 + 9 + 11)/3
    = 27/3
    = 9

    Hence, the correct answer is option (d) 9.

    Anurag Mishra Professor Answered on 25th February 2016.
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