The average of the first five multiples of 9 is:

Answer: Option B

$$\begin{array}{rl}& \text{Required}\text{average}\\ & =\frac{\text{total}\text{sum}\text{of}\text{multiple}\text{of}9}{5}\\ & =\frac{9+18+27+36+45}{5}\\ & =27\end{array}$$
Note that, average of 9 and 45 is also 27.
And average of 18 and 36 is also 27.