multiplicar inputs text

[alanmedbel]

algo asi como esto

Código HTML:

<script>
function calc(){
var por;
por = parseInt(document.getElementById('costo').value) * 1.65;
document.getElementById('pre1').value = por;
}
</script>
<table><form id="frmproducto" method="post" action="insertaProd.php" >
<tr>
<td>Clave:</td>
<td><input id="clave" type="text" size="10" maxlength="10"/></td></tr>
<tr>
<td>Descripcion:</td>
<td><input id="descrp" type="text" size="55" maxlength="65"/></td></tr>
<tr>
<td>Costo:</td>
<td><input id="costo" type="text" size="7" maxlength="8"/></td></tr>
<tr>
<td>Precio 1:</td>
<td><input id="pre1" type="text" size="7" maxlength="8" disabled="disabled" /></td></tr>
 
</td></tr>
<tr>
<td></td><td height="30"></td></tr>
<tr>
<td colspan="2" align="center"><p></p>
<button type="button" onclick="calc()"><img src="imgs/add_48.png" alt="Agrega" align="absmiddle"/>Agregar</button>&nbsp;
<button type="reset" ><img src="imagenes/edit-clear.png" alt="Restablecer campos" align="absmiddle" width="24" height="24"/> Limpiar</button>
</td></tr>
</form>
</table>