marc,
<!DOCTYPE html>
<html>
<head>
<title>Untitled</title>
<meta charset="utf-8">
<style type="text/css">
</style>
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.12.4/jquery.min.js"></script>
<script>
$(function() {
var s = $("#sel"), r = $("[name='rate']");
s.change(function() {
r.prop("checked", false).filter("[value='"+this.value+"']").prop("checked", true)
})
r.click(function() {
s.val(this.value)
})
});
</script>
</head>
<body>
<select id="sel" name="sel">
<option value="0">zero</option>
<option value="1">one</option>
<option value="2">two</option>
<option value="3" selected="selected">three</option>
</select>
<div id="rates">
<input type="radio" name="rate" value="1"> 1
<input type="radio" name="rate" value="2"> 2
<input type="radio" name="rate" value="3" checked="checked"> 3
</div>
</body>
</html>