How to multiply 2 td in javascript?

I have a table where one td gets 1 if a checkbox is checked and I would like to multiple this td with another and display it in a third one.

See the html here:

    <div>
    <input type="checkbox" id="fut1">check</input>
</div>
<table border="1" cellpadding="10" id="countit">
    <tr>
        <td id="td1"></td>
        <td id="td2">5000</td>
        <td id="td3"></td>
    </tr>
</table>

And here is the js:

$('#fut1').change(function () {
    if ($(this).is(":checked")) {
        $('#td1').text('1');
    } else {
        $('#td1').text('0');
    }
});

$('#td1').change(function () {
    var me = $('#td1').value;
    var ar = $('#td2').value;
    var sum = me * ar;
    $('#td3').text(sum);
});