Ajax request working but not displaying?

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PHP

Ajax

I'm having an issue with an ajax request. I have a created a quiz which goes through questions and when the user finishes it, it should call a request to an AJAX.PHP file to call out information. Please see my code below, i have run the ajax.php file and it is gathering up all the information. But in the tests.php page, when it finishes it shows nothing. also the ajax $("#quiz_form,#demo1").addClass("hide"); seems to work as nothing displays, but doesnt complete the next two functions below.

Can someone help?

AJAX REQUEST - in tests.php

What I have tried:

function submit(){
     $.ajax({
                    type: "POST",
                    url: "ajax.php",
                    data: $('form').serialize(),
                    success: function(msg) {
                      $("#quiz_form,#demo1").addClass("hide");
                      $('#result').show();
                      $('#result').append(msg);
                    }
     });

ajax.php

$response= $db->prepare("SELECT id,question_name,answer FROM questions");
$response->execute();

 $i=1;
 $right_answer=0;
 $wrong_answer=0;
 $unanswered=0;

 while($result=$response->fetch(PDO::FETCH_ASSOC)) {
// while($result=mysql_fetch_array($response)){ 
       if($result['answer']==$_POST["$i"]){
           $right_answer++;
       }else if($_POST["$i"]==5){
           $unanswered++;
       }
       else{
           $wrong_answer++;
       }
       $i++;
 }
 echo "<div id='answer'>";
 echo " Right Answer  : ". $right_answer."<br>";

 echo " Wrong Answer  : ". $wrong_answer."<br>";

 echo " Unanswered Question  : ". $unanswered."<br>";
 echo "</div>";