# Combined mean of two series $x_1\: and \: x_2$ when  $x_1 = 210,\: x_2 = 150, \: n_1=50, \: n_2=100$ is

$\begin {array} {1 1} (A)\;150 & \quad (B)\;160 \\ (C)\;170 & \quad (D)\;180 \end {array}$

Combined mean = $\large\frac{n_1x_1+n_2x_2}{n_1+n_2}$
$= \large\frac{50 \times 210 + 100 \times 150}{50+150}$
$\large\frac{10500+15000}{200}$
$= 170$