All Experts Answer

//index.php
<?php
    //Check for the existence of the cookie
    if(!empty($_COOKIE['passed_index'])){
      header("Location:q1.php");
    }

    if(array_key_exists("dad", $_POST)){
        $dad = $_POST["dad"];
        $correct_answer = "Fail";
        if($dad == $correct_answer){
            setcookie('passed_index', '1' ,time()+60*60*24); //This line sets the cookie for 1 year
            header("Location: q1.php");
        }else{
            $wrong="<div class='error'>Wrong answer</div>";
        }
    }
?>
<form action="index.php" method="post">
    <label>Enter your father's name:</label>
    <input autofocus required autocomplete="off" type="text" name="dad" placeholder="Bill">
    <input type="submit" value="Press me when you think you are right" />
    <?php
      echo $wrong;
    ?>
</form>

//q1.php
    <div>
        Hah! Just a lucky guess! I could probably do that if I was blindfolded and my hands were tied behind my back. Let's see if you can do another one.
    </div>
    <form action="q2.php" method="post">
        <label>Enter your mother's name:</label>
        <input autofocus required autocomplete="off" type="text" name="mom" placeholder="Billette"><br>
        <input type="submit" value="Poke me. I dare you.">
    </form>