SO fiddle

Test Fiddle mainly for SO Questions

by Nick Craver

HTML

<link rel="stylesheet" href="http://ajax.googleapis.com/ajax/libs/jqueryui/1.8.4/themes/overcast/jquery-ui.css">
<table>
<tr><td>ID</td><td>Mark</td>
<tr><td>1</td><td>40</td></tr>
<tr><td>2</td><td>35</td></tr>
<tr><td>1</td><td>52</td></tr>
</table>

JavaScript

function getTotal(id) {
    var total = 0;
    $("td:first-child").filter(function() { return this.innerHTML == id; })
        .next().each(function() { total += parseInt(this.innerHTML, 10); });
    return total;           
}
alert(getTotal(1));
alert(getTotal(2));