How to calculate the percentage of posts with a specific term

<?php

// Function to do the term count or post count calculations:
function get_post_count_for_term_and_post_type( $term_id, $taxonomy, $post_type ) {

  $taxquery = array();

  if ($term_id && $taxonomy) {
    $taxquery = array(
      array(
        'taxonomy' => $taxonomy,
        'field' => 'id',
        'terms' => $term_id,
      )
    );
  }

  // Build the args
  $args = array(
    'post_type' => $post_type,
    'posts_per_page' => -1,
    'tax_query' => $taxquery
  );

  // Create the query
  $query = new WP_Query( $args );
  $total = $query->found_posts;

  // Return the count
  return $total;

}

// Get the number of posts for the category with id 17. Fill in the term id, taxonomy and post type:
$termcount = get_post_count_for_term_and_post_type(17,'category','post');

// Get the total number of posts for the 'post' post type.  Fill in empty strings for the term id and taxonomy, and the post type in the last argument:
$postcount = get_post_count_for_term_and_post_type('','','post');

// Percentage of posts with term 17:
$percentage = $termcount / $postcount * 100 .'%';

echo $percentage;