One solution would be to divide your table into 20 columns of 5% width each, then use colspan on each real column to get the desired width, like this:
<html>
<body bgcolor="#14B3D9">
<table width="100%" border="1" bgcolor="#ffffff">
<colgroup>
<col width="5%"><col width="5%">
<col width="5%"><col width="5%">
<col width="5%"><col width="5%">
<col width="5%"><col width="5%">
<col width="5%"><col width="5%">
<col width="5%"><col width="5%">
<col width="5%"><col width="5%">
<col width="5%"><col width="5%">
<col width="5%"><col width="5%">
<col width="5%"><col width="5%">
</colgroup>
<tr>
<td colspan=5>25</td>
<td colspan=10>50</td>
<td colspan=5>25</td>
</tr>
<tr>
<td colspan=10>50</td>
<td colspan=6>30</td>
<td colspan=4>20</td>
</tr>
</table>
</body>
</html>