jQuery IF Formula with Multiple Conditions & Number Range

I need to set several if statements using jquery:

if amt (variable) is between 0 to 5000 change input value

else if amt is between 5001 to 17999 change input value

else change input value

My else if doesn't seem to work and I always end-up with the else return.

*my input type is set to number.

        $('#pledge').submit(function(){ 
        var amt = $("#donation").val();
        if ((amt <= '17999' && amt >= '5001')) {   
            $('#priority').val('2');
        }
        else if (amt <= '0' && amt >= '5000') {
            $('#priority').val('2');
        }
        else {$('#priority').val('3');}
         });

It always returns priority = 3.