How to sum radio button values using either Javascript or jQuery?

I would do it like that:

function calcscore(){
    var score = 0;
    $(".calc:checked").each(function(){
        score+=parseInt($(this).val(),10);
    });
    $("input[name=sum]").val(score)
}
$().ready(function(){
    $(".calc").change(function(){
        calcscore()
    });
});

See this js fiddle example

the html structure is equal to yours, only i added a class calc, so that i can selected them easier.