Relative number of post in category

Are you using the main query or a custom WP_Query for displaying the posts?

If so :

 $wp_query->found_posts; //Main query
 $wp_query->current_post; // current post index

or

 $my_wp_query->found_posts; //custom wp_query object - total found posts
 $my_wp_query->current_post; // current post index

So, example

 if( have_posts() ) : while( have_posts() ) : the_post();
 ?>
      <p>The post <?php the_title(); ?> is <?php echo $wp_query->current_post; ?>th of <?php echo $wp_query->found_posts; ?> in category <?php echo 'your cat here'; ?></p>

 <?php endwhile; endif; ?>