title: jQuery - Perform a Calculation
body: <p>I have the following 3 input fields in a form:</p>
  
  <pre><code>&lt;input id="a" name="a" type="text" /&gt;
  &lt;input id="b" name="b" type="text" /&gt;
  &lt;input id="c" name="c" type="text" /&gt;
  </code></pre>
  
  <p>and the following paragraph:</p>
  
  <pre><code>&lt;p id="grand_total"&gt;&lt;/p&gt;
  </code></pre>
  
  <p>I want to multiply the three text inputs together and fill in the <code>grand_total</code> with the result.</p>
  
  <p>I only want the result to appear when we have filled in all three text inputs with integers between 0 and 1000.</p>
  
  <p>Also if any of the text field values are changed to another valid integer then I want the <code>grand_total</code> to be re-calculated.  Any help would be much appreciated, thanks.</p>