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<html><head><style>table, th, td { border: 1px solid black;}</style></head><body><p>Click the button to change the value of the colspan attribute, from 2 to 1, of th with id "myTh".</p><table> <tr> <th id="myTh" colspan="2">Month</th> <th>Savings</th> </tr> <tr> <td>January</td> <td>$100</td> </tr> <tr> <td>February</td> <td>$100</td> </tr></table><br> <button onclick="myFunction()">Try it</button><script>function myFunction() { document.getElementById("myTh").colSpan = "1";}</script></body></html>