calculation problem

Hi, guys:
I am a JavaScript newbie.
I am trying to do calculations using JavaScript, I try to
get total based on user inputted amount and rate values,
and get amount based on user inputted total and rate; rate value
is actually preset:

function calcTotal(form)
{
var amount = form.amount.value;
var rate = form.rate.value;
var total = form.total.value;

form.total.value = (parseFloat(form.amount.value) * parseFloat(form.rate.value));
}

function calcAmount(form)
{
var rate = form.rate.value;
var total = form.total.value;
var amount = form.amount.value;

form.amount.value = (parseFloat(form.total.value) / parseFloat(form.rate.value));
}

<input type=”text” name=”amount” maxlength=”16″ size=”40″ value=”” onchange=”calcAmount(this.form)”>
</td>

<input type=”text” name=”total” maxlength=”16″ size=”20″ value=”” onchange=”calcTotal(this.form)”>
</td>
<input type=”text” name=”rate” maxlength=”10″ size=”15″ value=”1.50″>

but I keep getting NaN if I input one number into either total textbox
or amount textbox. What did I do wrong?

regards,

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