Variance and average

Of the 40 values were calculated average mx = 7.5 and variance sx = 2.25. After the control was found to lack the two items of the values of x41 = 3.8 and x42=7. Correct the above characteristics (mx and sx).

Correct result:

m2 =  7.4
r2 =  2.4552

Solution:

m1=7.5 r1=2.25 n1=40  x41=3.8 x42=7 n2=42   m2=(n1 m1+x41+x42)/n2=(40 7.5+3.8+7)/42=375=7.4
r1=n1 (xm1)2/n1  x=r1+m1=2.25+7.5=9  r2=(n1 (xm1)2+(x41m2)2+(x42m2)2)/n2=(40 (97.5)2+(3.87.4)2+(77.4)2)/42=1289525=2.4552



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