cout elements by class and status, jquery
<p>i have this checkbox:</p>

<pre><code>&lt;input type="checkbox" id="cb_1" class="cat" name="cat1" value="1"&gt;
&lt;input type="checkbox" id="cb_2" class="cat" name="cat2" value="1" checked&gt;
&lt;input type="checkbox" id="cb_3" class="dog" name="dog" value="1"&gt;
&lt;input type="checkbox" id="cb_4" class="cat" name="cat3" value="1" checked&gt;
&lt;input type="checkbox" id="cb_5" class="dog" name="cat2" value="1" checked&gt;
</code></pre>

<p>How count checkbox where class is "cat" and this checkbox is selected (with jQuery)?</p>
