something like that...
Code:
<html>
<body>
<script language="JavaScript">
function calculate()
{
var A1 = document.Qty_form.quanity.value;
var A2 = document.Qty_form.price.value;
var A3 = (A1*A2);
document.Qty_form.total.value = A3;
}
</script>
<html>
<body>
<form name="Qty_form" onChange=calculate();>
<input type="text" name="quanity">
X
<input type="text" name="price">
=
<input type="text" name="total" >
</form>
<style type="text/css">
</body>
</html>
seems to be working to me. you will need to finish the action of changing the respective value by either clicking out of the field or hitting enter.