[tex]11. \: we \: know \: that \\ \frac{sum \: of \: all \: quantities}{number \: of \: quantities} = mean \\ => \frac{7 + 11 + 13 + 6 + 8 + x}{6} = 8 \\ = > \frac{45 + x}{6} = 8 \\ = > 45 + x = 8 \: \times 6 \\ = > 45 + x = 48 \\ = > x = 48 - 45 \\ = > x = 2 \\ \\ 12. we \: know \: that \\ \frac{sum \: of \: all \: quantities}{number \: of \: quantities} = mean \\ => \frac{2 + 5 + 1.3 + 2.2 + x}{5} = 1.8 \\ = > \frac{10.5 + x}{5} = 1.8 \\ = > 10.5 + x = 5 \times 1.8 \\ = > 10.5 + x = 9 \\ = > x = 9 - 10.5 \\ = > x = - 1.5 \\ [/tex][/tex]
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