The mean and standard deviation of 100 items are 50 and 4, respectively then the sum of all squares of the items is
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A useful rearranged form of the variance formula to memorize for direct calculation is: $\sum x_i^2 = N \cdot (\sigma^2 + \mu^2)$. This allows you to plug numbers straight in: $100 \times (16 + 2500) = 251600$.