The average of the first 18 positive multiples of 11 is:

The correct option is 104.5.

To find the average of the first 18 positive multiples of 11, we first list these multiples. The first positive multiple of 11 is $11\times 1=11$, the second is $11\times 2=22$, and so on, up to the 18th multiple which is $11\times 18=198$.

These multiples form an arithmetic progression (AP):
11, 22, 33, ..., 198

The formula for the average of an arithmetic progression is given by the average of its first and last terms:
$\text{Average}=\frac{\text{First term}+\text{Last term}}{2}$

Substituting the first term (11) and the last term (198) into the formula, we get:
$\text{Average}=\frac{11+198}{2}$

Simplifying the numerator:
$\text{Average}=\frac{209}{2}$

Calculating the final division:
$\text{Average}=104.5$

Thus, the average of the first 18 positive multiples of 11 is 104.5.