Bài tập 54 trang 93 SGK Toán 11 NC

Ta có:

\(\begin{array}{*{20}{l}}
{E\left( X \right) = 15.\frac{3}{{14}} + 18.\frac{{27}}{{56}} + 21.\frac{{15}}{{56}} + 24.\frac{1}{{28}} = 18,375}\\
\begin{array}{l}
V\left( X \right) = {\left( {15 - 18,375} \right)^2}.\frac{3}{{14}} + {\left( {18 - 18,375} \right)^2}.\frac{{27}}{{56}}\\
 + {\left( {21 - 18,375} \right)^2}.\frac{{15}}{{56}} + {\left( {24 - 18,375} \right)^2}.\frac{1}{{28}} \approx 5,484
\end{array}\\
{\sigma \left( X \right) = \sqrt {V\left( X \right)}  \approx 2,342}
\end{array}\)

-- Mod Toán 11 HỌC247