
A.
(frac{2}{3}) 
B.
(frac{2}{3}sqrt{3}) 
C.
(sqrt{frac{2}{3}}) 
D.
(sqrt{frac{3}{2}})
Correct Answer: Option C
Explanation
(x) = (frac{5 + 6 + 7}{3})
= (frac{18}{3})
= 6
(begin{array}{cc} scores(X) & text{d = (x – x) deviation} & (deviation)^2\hline 5 & 5 – 6 & 1\ 6 & 6 – 6 & 0 \ 7 & 7 – 6 & 1\ hline & & 2end{array})
S.D (sqrt{frac{sum d^2}{n}}) where d = deviation = (x – x)
= (sqrt{frac{2}{3}})