Edit in JSFiddle

window.$ = function (selector) { return document.querySelectorAll(selector); };

var cells = $("#score>tbody>tr>td:nth-of-type(2)");

// cells is equal to:
// [<td>87% </td>, <td>78%</td>, <td>81%</td>]

 //debugger
<table id="score">
  <thead>
    <tr>
      <th>Test</th>
      <th>Result</th>
    </tr>
  </thead>
  <tfoot>
    <tr>
      <th>Average</th>
      <td>82%</td>
    </tr>
  </tfoot>
  <tbody>
    <tr>
      <td>A</td>
      <td>87%</td>
    </tr>
    <tr>
      <td>B</td>
      <td>78%</td>
    </tr>
    <tr>
      <td>C</td>
      <td>81%</td>
    </tr>
  </tbody>
</table>