Calculation of ID card verification code

It turns out that the last X in my ID is actually 2.

 public function id_verify($my_id) {

 $coefficient = array(7,9,10,5,8,4,2,1,6,3,7,9,10,5,8,4 ,2);

 $remainder_map = array(1,0,'X',9,8,7,6,5,4,3,2);

 $count = 0;

 for ($i= 0; $i < 17; $i++) {

 $count += $my_id[$i] * $coefficient[$i];
 }

 $remainder = $count % 11;

 if ($my_id [17] == $remainder_map[$remainder]){

 echo 'true';
 }else{

 echo 'false';
 }
 }