title: Add number of radio buttons selected (in php/js)
body: <p>I have 5 sets of radio buttons, set1, set2, set3, set4, set5. Values are yes/no for each.</p>
  
  <p>I need the number of yes's to be shown in a hidden text box.. ie 1,2,3,4 or 5, and obviously change as people select different options..</p>
  
  <pre><code>&lt;input type="radio" name="set1" id="set1_no" value="no"&gt;
  &lt;input type="radio" name="set1" id="set1_yes" value="yes"&gt;
  
  &lt;input type="radio" name="set2" id="set2_no" value="no"&gt;
  &lt;input type="radio" name="set2" id="set2_yes" value="yes"&gt;
  
  &lt;input type="radio" name="set3" id="set3_no" value="no"&gt;
  &lt;input type="radio" name="set3" id="set3_yes" value="yes"&gt;
  
  &lt;input type="radio" name="set4" id="set4_no" value="no"&gt;
  &lt;input type="radio" name="set4" id="set4_yes" value="yes"&gt;
  
  &lt;input type="radio" name="set5" id="set5_no" value="no"&gt;
  &lt;input type="radio" name="set5" id="set5_yes" value="yes"&gt;
  
  
  &lt;input type="hidden" name="number_of_yes" value="" readonly="readonly"&gt;
  </code></pre>