Let the mean of \( 6 \) observations \( 1, 2, 4, 5, x \) and \( y \) be \( 5 \) and their variance be \( 10 \). Then their mean deviation about the mean is equal to:
\( \dfrac{8}{3} \)
\( \dfrac{7}{3} \)
\( \dfrac{10}{3} \)
\( 3 \)