Access nth column of table
<p>I have a table with the following structure and data</p>

<pre><code>&lt;tr&gt;
&lt;td&gt;&lt;input id="c1" type="checkbox"/&gt;&lt;/td&gt;
&lt;td&gt;342&lt;/td&gt;
&lt;td&gt;24&lt;/td&gt;
&lt;td&gt;Jeff&lt;/td&gt;
&lt;/tr&gt;
&lt;tr&gt;
&lt;td&gt;&lt;input id="c2" type="checkbox"/&gt;&lt;/td&gt;
&lt;td&gt;343&lt;/td&gt;
&lt;td&gt;29&lt;/td&gt;
&lt;td&gt;Libo&lt;/td&gt;
&lt;/tr&gt;
</code></pre>

<p>I want to calculate total value of the third column of all rows, which are checked. So assuming both rows above are checked, the value of third column will be 24+29=53</p>
