WordPress Post # of # filtered by category slug

I want to show post #4/100 at the top for each post

for which I’m using following code

function updateNumbers() {
/* numbering the published posts: preparation: create an array with the ID in sequence of publication date, /
/ save the number in custom field 'incr_number' of post with ID  /
/ to show in post (within the loop) use <?php echo get_post_meta($post->ID,'incr_number',true); ?>
/ alchymyth 2010 */
global $wpdb;
$querystr = "SELECT $wpdb->posts.* FROM $wpdb->posts WHERE $wpdb->posts.post_status = 'publish' AND $wpdb->posts.post_type = 'post' ";
$pageposts = $wpdb->get_results($querystr, OBJECT);
$counts = 0 ;
if ($pageposts):
foreach ($pageposts as $post):
setup_postdata($post);
$counts++;
add_post_meta($post->ID, 'incr_number', $counts, true);
update_post_meta($post->ID, 'incr_number', $counts);
endforeach;
endif;
}  

add_action ( 'publish_post', 'updateNumbers' );
add_action ( 'deleted_post', 'updateNumbers' );
add_action ( 'edit_post', 'updateNumbers' );

<?php echo get_post_meta($post->ID,'incr_number',true); ?>

This code seems to work fine for me but I just want to filter posts by category slug & only count posts for that particular category

Thanks