este es el formulario
Código:
  
y este java<input type="text" id="txt7" onKeyUp="sum();" size="8" value="0"/> <input type="text" id="txt27" onKeyUp="sum();"size="8" value="0"/> <input type="text" id="txt37" onKeyUp="sum();" size="8"value="0"/> <input type="text" id="txt47" onKeyUp="sum();" size="8"value="0"/> <input type="text" id="txt55" onKeyUp="sum();" size="8"value="0"/> <input type="text" id="txt65" onKeyUp="sum();" size="8"value="0"/> <input type="text" id="txt75" onKeyUp="sum();" size="8"value="0"/> <input type="text" id="txt8" value="0"/>
Código:
  
 
function sumtotal() {
   
    var txtFirstNumberValue = document.getElementById('txt7').value;
    var txtSecondNumberValue=document.getElementById('txt27').value;
    var txtThirdNumberValue = document.getElementById('txt37').value;
    var txtfourthNumberValue =document.getElementById('txt47').value; 
    var txtfifthNumberValue=document.getElementById('txt55').value;
    var txtsixthNumberValue=document.getElementById('txt65').value;
    var txtseventhNumberValue=document.getElementById('txt75').value;
    if (txtFirstNumberValue == "") txtFirstNumberValue = 0;   
    if (txtSecondNumberValue == "") txtSecondNumberValue = 0;
    if (txtThirdNumberValue == "") txtThirdNumberValue = 0;
    if (txtfourthNumberValue == "") txtfourthNumberValue = 0;    
    if (txtfifthNumberValue == "") txtfifthNumberValue = 0;
    if (txtsixthNumberValue == "") txtsixthNumberValue = 0;
    if (txtseventhNumberValue == "") txtseventhNumberValue = 0;
var result = 
Number(txtFirstNumberValue) + 
Number(txtSecondNumberValue) + 
Number(txtThirdNumberValue) + 
Number(txtfourthNumberValue) +
Number(txtfifthNumberValue)+ 
Number(txtsixthNumberValue)+ 
Number(txtseventhNumberValue);
    if (!isNaN(result)) {
        document.getElementById('txt8').value = result;
    }
}
 
 



