If mean of squares of deviations of a set of n observations about -2 and 2 are 18 and 10 respectively, then standard deviation of this set of observations is

If mean of squares of deviations of a set of n observations about -2 a

1.	If mean of squares of deviations of a set of n observations about -2 and 2 are 18 and 10 respectively, then standard deviation of this set of observations is
Answer» `sum(x_i-22)^2/N` `sum(x_i+2)^2/N=18-(1)` `sum(x_i-2)^2/N=10-(2)` `sum(x_i^2+4+4x_i)=18N` `sumx_i^2+sum4+4sumx_i=18N` `sumx_i^2+4sumx_i=14N-(3)` `sumx_1^2+4N-4sumx_i=10N` `sumx_i^2-4sumx_i=6N-(4)` adding equation 3 and 4 `2sumx_i^2=20N` `sumx_i^2=10N` subtracting equation 2 from 3 `8sumx_i=8N` `sumx_i=N` `sumx_1/N=1` `SD=sqrt(sum(x_i-x)^2/N)` `=sum(x_i-mu)^2/N` `=sum(x_i^2+mu^2-2x_imu)/N` `=(11N-2N)/N=9N/N=9` square of standard deviation=9 standard deviation=3.

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If mean of squares of deviations of a set of n observations about -2 and 2 are 18 and 10 respectively, then standard deviation of this set of observations is

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