If an experiment with 15 observations on $x$ the following results were available: $\Sigma x^2=2830 \: \Sigma x = 170$. One observation that was 20 was found to be wrong and was replaced by the correct value 30. The corrected variance is

Question

$\begin {array} {1 1} (A)\;8.33 & \quad (B)\;78.00 \\ (C)\;188.66 & \quad (D)\;177.33 \end {array}$