高分求救对动态表格的计算问题,
表格见图

如图所示,在输入完每行的qty及price之后,自动计算乘积并填入到total中,即a=a1*a2
并且在填入total中之后自动更新amount的值,该值为total的和,即amount=a+b+c,
add是添加一行的意思,如果是四行,那就是amount=a+b+c+d

请高手指教这二个计算该如何写,下面是已知的表格动态添加部分的代码:
function AddRecord()  
{  
  var row = tlist.insertRow(tlist.rows.length-2);
  row.className='tit3'; 
  var i = row.rowIndex;  
  var col = row.insertCell(0);  
  col.innerHTML = "<input type='text' name='fno"+i+"' size=12 maxlength=12>";  
  col = row.insertCell(1);  
  col.innerHTML = "<input type='text' name='fdesc"+i+"' size=32 maxlength=100>";  
  col = row.insertCell(2);  
  col.innerHTML = "<input type='text' name='fqty"+i+"' size=7 maxlength=7 value='0' onchange='chtotal(i);'>";  
  col = row.insertCell(3);  
  col.innerHTML = "<input type='text' name='fprice"+i+"' size=6 maxlength=6 value='0' onchange='chtotal(i);'>";  
  col = row.insertCell(4);  
  col.innerHTML = "<input type='text' name='finners"+i+"' size=4 maxlength=4>";  
  col = row.insertCell(5);  
  col.innerHTML = "<input type='text' name='fouters"+i+"' size=4 maxlength=4>";  
  col = row.insertCell(6);  
  col.innerHTML = "<input type='text' name='ftotal"+i+"' size=8 readonly >";  
  col = row.insertCell(7);  
  col.innerHTML = "<input type='text' name='fremarks"+i+"' size=20 maxlength=100>";
  col = row.insertCell(8);  
  col.innerHTML = "<input type='button' value='删除' id='delbutton"+i+"' onclick='delrecord(this);'>";  
  document.getElementById('delButton'+(i-1)).disabled=true; //这里将上一个button设置为无效
}

------解决方案--------------------
改了一下，这下完整了：

<table width="760" border="0" cellspacing="1" cellpadding="0" class="tb" id="tlist">
<tr class="tit2" align='center'>
<td>ITEM NO </td> <td>ITEM DESCRIPTION </td> <td>QTY </td> <td>PRICE </td> <td>INNER </td> <td>OUTER </td> <td>TOTAL </td> <td>REMARKS </td> <td>操作 </td>
</tr>
<tr class="tit3" align='center'>
<td> <input type="text" id="fno1" name="fno1" size=12 maxlength=12> </td>
<td> <input type="text" id="fdesc1" name="fdesc1" size=32> </td>
<td> <input type="text" id="fqty1" name="fqty1" size=7 maxlength=7 value='0' onchange='chtotal(1);'> </td>
<td> <input type="text" id="fprice1" name="fprice1" size=6 maxlength=6 value='0' onchange='chtotal(1);'> </td>
<td> <input type="text" id="finners1" name="finners1" size=4 maxlength=4> </td>
<td> <input type="text" id="fouters1" name="fouters1" size=4 maxlength=4> </td>
<td> <input type="text" id="ftotal1" name="ftotal1" size=8 readonly > </td>
<td> <input type="text" id="fremarks1" name=&quo