The average of all the odd integers between 2 an 22 is ?

Answer: Option B

Series → 3 + 5 + 7 . . . . . 21
Total numbers
$$\frac{\text{Last term }-\text{ First term}}{\text{Difference}}$$     + 1
= $$\frac{21-3}{2}$$ + 1
= $$\frac{18}{2}$$ + 1
= 10
Sum of series
$$\begin{array}{rl}& =\frac{n}{2}\left[2a+\left(n-1\right)d\right]\\ & =\frac{10}{2}\left[2\times 3+\left(10-1\right)\times 2\right]\\ & =5\left[6+9\times 2\right]\\ & =5\times 24\\ & =120\end{array}$$
Average = $$\frac{120}{10}$$ = 12