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/themes/dot-luv/jquery-ui.css">
 <table id="ctl00_ContentPlaceHolder1_ctl02_rblDependants"  border="0" style="border-width:0px;">
        <tr>
            <td><input id="ctl00_ContentPlaceHolder1_ctl02_rblDependants_0" type="radio" name="ctl00$ContentPlaceHolder1$ctl02$rblDependants" value="Yes" /><label for="ctl00_ContentPlaceHolder1_ctl02_rblDependants_0">Yes</label></td>
        </tr><tr>
            <td><input id="ctl00_ContentPlaceHolder1_ctl02_rblDependants_1" type="radio" name="ctl00$ContentPlaceHolder1$ctl02$rblDependants" value="No" checked="checked" /><label for="ctl00_ContentPlaceHolder1_ctl02_rblDependants_1">No</label></td>
        </tr>
</table>

<div id="ctl00_ContentPlaceHolder1_ctl02_pnlDependants">

    <div class="QuestionWrapper">
    
        <div class="Question">
            <label for="">No. of Dependants</label>
        </div>
        <div class="Answer">
            <input name="ctl00$ContentPlaceHolder1$ctl02$txtNoOfDependants" type="text" maxlength="2" id="ctl00_ContentPlaceHolder1_ctl02_txtNoOfDependants" />
        </div>
        <div class="ClearFloat"></div>
    </div>
</div>

JavaScript

$("table[id$=_rblDependants] :radio").change(function() {
    $(this).closest('table').next().toggle(this.checked && this.value == 'Yes');
}).change();