Text Box Calculation

[Clinton]

I have a form. If I put in 5 for 'Quantity' and '1.00' for UnitCost when I go to TotalCost I want it to automatically compute the total. In this case 5.00. Make sense? How do I do this?

 

<tr><td>Quantity:</td><td>
<input type="text" name="Quantity">
</td></tr>
<tr><td>Unit Cost:</td><td>
<input type="text" name="UnitCost">
</td></tr>
<tr><td>Total Cost:</td><td>
<input type="text" name="TotalCost">
</td></tr>

 

 

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P.S. I found this which is probably what I want but I'm not sure how to modify it for my purposes:

 

<script language="javascript1.1">

        function summate() {

        var tot=0

        for (var i=1; i <= 5; i++) {

        var id = "txt"+i;

            tot = tot + document.getElementById(id).value*1;

        }

        document.getElementById("tot").value = tot;

        }

</script>