The average of all the odd integers between 2 an 22..

Series → 3 + 5 + 7 . . . . . 21 Total numbers $\begin{aligned}&\frac{\text{ Last term }-\text{ First term }}{\text{ Difference }}+1\\ &=\frac{21-3}{2}+1\\ &=\frac{18}{2}+1\\ &=10\end{aligned}$ $\begin{array}{l}\text{ Sum of series }\\ =\frac{n}{2}[2a+(n-1)d]\\ =\frac{10}{2}[2\times3+(10-1)\times2]\\ =5[6+9\times2]\\ =5\times24\\ =120\\ \text{ Average }=\large\frac{120}{10}\\ =12\end{array}$