Get posts after calculating meta key

Assuming meta_count is another column in your postmeta table below query should get you the posts based on meta_value/meta_count calculation.

$postids=$wpdb->get_col( $wpdb->prepare( 
    "SELECT post_id
    FROM $wpdb->postmeta
    ORDER BY (meta_value/meta_count)
    LIMIT 10
    "
) );

The result $postids would be an array. You will have to declare $wpdb as a global variable before you use this query.