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.