For 30 observations, the recorded summary statistics are ∑x=600\sum x=600∑x=600 and ∑x2=13200\sum x^2=13200∑x2=13200. A value of 20 was incorrectly recorded as 40.
Find the corrected values of ∑x \sum x\,∑x and ∑x2\sum x^2∑x2.
Calculate the corrected variance.