$(document).ready(function(){

            $('.txt' ).live('keyup', function(){
            calculateSum();
            });
        });

    function calculateSum() {

        var sum = 0;
        //iterate through each textboxes and add the values
        $(".txt").each(function() {

            //add only if the value is number
            if(!isNaN(this.value) && this.value.length!=0) {
                sum += parseFloat(this.value);
            }

        });
        //.toFixed() method will roundoff the final sum to 2 decimal places
        $("#sum").html(sum.toFixed(2));
    }