Let $\bar{x}$ be the mean of $x_{1}, x_{2}, \ldots, x_{n}$ and $\bar{y}$ be the mean of $y_{1}, y_{2}, \ldots, y_{n}$.
If $\bar{z}$ is the mean of $x_{1}, x_{2}, \ldots, x_{n}, y_{1}, y_{2}, \ldots, y_{n}$, then $\bar{z}=?$
(a) $(\bar{x}+\bar{y})$
(b) $\frac{1}{2}(\bar{x}+\bar{y})$
(c) $\frac{1}{n}(\bar{x}+\bar{y})$
(d) $\frac{1}{2 n}(\bar{x}+\bar{y})$
(b) $\frac{1}{2}(\bar{x}+\bar{y})$
$\bar{z}=\frac{\left(x_{1}+x_{2}+\ldots+x_{n}\right)+\left(y_{1}+y_{2}+\ldots+y_{n}\right)}{2 n}$
Given :
$\bar{x}=\frac{x_{1}+x_{2}+\ldots \ldots x_{n}}{n}$
$\Rightarrow x_{1}+x_{2}+\ldots \ldots+x_{n}=n \bar{x}$
and
$\bar{y}=\frac{y_{1}+y_{2}+\ldots \ldots+y_{n}}{n}$
$\Rightarrow y_{1}+y_{2}+\ldots \ldots+y_{n}=n \bar{y}$
$\therefore \bar{z}=\frac{n \bar{x}+n \bar{y}}{2 n}$
$=\frac{1}{2}(\bar{x}+\bar{y})$