In an experiment with 15 observations on $x$, the following results were available <br> $\displaystyle\sum x^2 = 2830, \; \displaystyle\sum x = 170$ <br> One observation that was 20, was found to be wrong and was replaced by the correct value 30. Then the corrected variance is :

Question

( A ) $177.33$
( B ) $188.66$
( C ) $8.33$
( D ) $78.00$