$value = str_replace("%RATINGS_SCORE%", $post_ratings_score, $value);

$post_ratings_score = $post_ratings_score + rand(5, 15);

<?php

/* Plugin Name: fr */

define( 'USERS_MIN', 10 );
define( 'USERS_MAX', 100 );
define( 'SCORE_MIN', 3 );
define( 'SCORE_MAX', 5 );

register_activation_hook( __FILE__, 'fake_rating');

function fake_rating() {
   set_time_limit(0);
   $types = array('post', 'page', 'attachment');
   foreach($types as $type) {
      $posts = get_posts( array( 'posts_per_page' => -1, 'post_type' => $type ) );
      foreach($posts as $post) {
         $ratings_users = rand( USERS_MIN, USERS_MAX );
         $ratings_score = rand( USERS_MIN * SCORE_MIN, $ratings_users * SCORE_MAX );
         update_post_meta( $post->ID, 'ratings_users', $ratings_users );
         update_post_meta( $post->ID, 'ratings_score', $ratings_score );
         update_post_meta( $post->ID, 'ratings_average', $ratings_score / $ratings_users );
      }
   }
}