jquery: how to check if all radio buttons in a div are selected

Question

my html looks like this

Answer 1

$(":radio").change(function() {
    var names = {};
    $(':radio').each(function() {
        names[$(this).attr('name')] = true;
    });
    var count = 0;
    $.each(names, function() { 
        count++;
    });
    if ($(':radio:checked').length === count) {
        alert("all answered");
    }
}).change();

Demo: http://jsfiddle.net/yFaAj/15/