Arithmetic mean ( $\overline{x}$ )

=

$\frac{x_1+x_2+x_3+x_4+x_5+x_6+\cdots +x_n}{n}=\frac{{\displaystyle {\sum }_{i=1}^n{x}_i}}{n}$

$P_{av}$

=

$\frac{P_1+P_2+P_3+P_4+P_5+P_6+\cdots +P_n}{n}=\frac{{\displaystyle {\sum }_{i=1}^n{P}_i}}{n}$

$P_{av}$

=

$\frac{P_1+P_2+P_3+P_4+P_5+P_6+P_7+P_8+P_9+P_{10}+P_{11}+P_{12}}{12}$