Arithmetic mean ( $\bar{x}$ )	=	$\frac{x_{1} + x_{2} + x_{3} + x_{4} + x_{5} + x_{6} + \dots + x_{n}}{n} = \frac{\sum_{i = 1}^{n} x_{i}}{n}$
$T_{a v}$	=	$\frac{T_{1} + T_{2} + T_{3} + T_{4} + T_{5} + T_{6} + \dots + T_{n}}{n} = \frac{\sum_{i = 1}^{n} T_{i}}{n}$
$T_{a v}$	=	$\frac{T_{1} + T_{2} + T_{3} + T_{4} + T_{5} + T_{6} + T_{7} + T_{8} + T_{9} + T_{10} + T_{11} + T_{12}}{12}$