If the arithmetic mean of 7, 9, 11, 13, x, 21 is 13, find the value of x.

Sum of numbers = 7 + 9 + 11 + 13 + x + 21 = 61 + x


Number of observation = 6


Arithmetic Mean =


= 13 =


= 61 + x = 13 × 6 = 78


= x = 78 – 61 = 17.


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