新GRE考試數(shù)學(xué)學(xué)習(xí)策略：standard variation

standard variation
    一組數(shù)中，每個(gè)數(shù)與平均數(shù)之差的平方和，再除以這組數(shù)的個(gè)數(shù)n
    例： standard variation of 0,2,5,7,6 is: _ 2 2 2 2 2_
    |_(0-4) +(2-4)+(5-4)+(7-4)+(6-4)_|/5=6.8