Let the random variable x be equally likely to assume any of the values 1/12, 1/6, or 1/4. determine the mean and variance of x.

The mean of x is
  (1/3)(1/12 + 1/6 + 1/4) = 1/6

The mean of the squares is
  (1/3)((1/12)² + (1/6)² + (1/4)²) = 7/216

The variance is the difference between the mean square and the square of the mean.
  7/216 -(1/6)² = 1/216

The mean of x is 1/6.
The variance of x is 1/216.