[html] html table cell width for different rows

with 5 columns and colspan, this is possible (click here) (but doesn't make much sense to me):

<table width="100%" border="1" bgcolor="#ffffff">
    <colgroup>
        <col width="25%">
        <col width="25%">
        <col width="25%">
        <col width="5%">
        <col width="20%">
    </colgroup>
    <tr>
        <td>25</td>
        <td colspan="2">50</td>
        <td colspan="2">25</td>     
    </tr>
    <tr>
        <td colspan="2">50</td>
        <td colspan="2">30</td>
        <td>20</td>
    </tr>
</table>