Grade a 20 question quiz and provide percentage correct

// Chris Hajer 21 August 2012
// reference http://www.gravityhelp.com/forums/topic/gravity-forms-quiz-help-needed#post-71088
add_action('gform_pre_submission', 'social_media_quiz_score');
function social_media_quiz_score ($form) {
        // change the number 2 here to your form ID
        // if this is not form 2, don't do any processing
        if($form['id'] != 2)
                return $form;

        // otherwise ...
        $score = 0;

        // my radio button inputs are numbered 1 to 20.  Change the beginning
        // and ending number in this loop to match your actual input numbers
        for($i=1; $i<=20; $i++) {
                // add the value of the $_POST value for input 1 to input 20
                $input  = 'input_' . $i;
                $score += rgpost($input);
        }

        // update the hidden 'Score' field with our calculated score
        $_POST['input_25'] = (int)($score * 5);
        switch($score) {
                // my "admin only" Rating field to hold the display message based on the score is input_24
                case 0:
                case 1:
                case 2:
                case 3:
                case 4:
                case 5:
                        $_POST['input_24'] = '5 or fewer correct answers: You really don\'t know much about social media.';
                        break;
                case 6:
                case 7:
                case 8:
                case 9:
                case 10:
                        $_POST['input_24'] = '6 to 10 correct answers: I guess you know a little bit about social media.';
                        break;
                case 11:
                case 12:
                case 13:
                case 14:
                case 15:
                        $_POST['input_24'] = '11 to 15 correct answers: You seem to know what you\'re talking about when it comes to social media.';
                        break;
                default:
                        $_POST['input_24'] = 'More than 15 correct answers: You might possibly know as much as I do about social media.  Maybe I should hire you.';
        }
        // return the form object
        return $form;
}