将两个数字相加，然后使用php和ajax与另一个相乘

Question

I am trying to add two numbers than multiply with another number whenever a keyup happens in the textboxes of those three numbers. I am trying to do this using php and ajax. My addition code is these:

My html code:

<form method="post">
  adult <input type="date" name="adult" id="adult" class="counter">
  child <input type="date" name="child" id="child" class="counter">
  amount <input type="date" name="amount" id="amount" class="counter">
</form>
<div id="showTotal"></div>

My jquery code:

 $(document).ready(function(){
  $(".counter").on('change keyup paste', function(e)
  {
   var number =
    {
        numad:$("#adult").val(),
        numch:$("#child").val(),
        numamo:$("#amount").val(),
        is_ajax:1
    };
    $.ajax(
    {
       type:"post",
       url:"process.php",
       data: number,
       dataType:"json",
       success:function(counter)
       {
           $("#showTotal").html(counter);
       }
    });
    return false;
   });
  }); 

process.php page:

<?php
 if(isset($_POST["numad"],$_POST["numch"],$_POST["numamo"]))
 {
   $adultnum = $_POST["numad"];
   $childnum = $_POST["numch"];
   $amountnum = $_POST["numamo"];

   $addtotal = $adultnum + $childnum * $amountnum;
   echo json_encode($addtotal);
 }

?>

This code id not working

Answer 1

Skip PHP and do it with JavaScript only:

.....
var total = $("#adult").val() + $("#child").val() * $("#amount").val();
$("#showTotal").html(parseInt(total));
.....