rn</span> source.Select(selector).Average();     <br />} </div>  <p>Salient points:</p>  <ul>   <li>Again I&#39;m using Select to make the implementation of the overloads with selectors trivial </li>    <li>I&#39;ve cast <em>both</em> operands of the division when calculating the average, just for clarity. We could get away with either of them. </li>    <li>In the case of the conditional operator, I could actually <em>just</em> cast one of the division operators to &quot;double?&quot; and then remove <em>bo