php问题来帮忙

$a=array (

   '14' => array ( 'ok' => 1 ,'err' => 1 ), 
   '15' => array ( 'ok' => 1 ,'err' => 0 ), 
   );

function ok_err_errate($errrate,$a){

   $arr_id=array(); 
   foreach ($a as $k=>$values) {
           foreach ($values as $data1) {
               if($data1['err']/($data1['ok']+$data1['err'])*100>=$errrate){
              $arr_id[]=$k;
          }
           }

   }
    return $arr_id;
}
$b =ok_err_errate(50,$a);
print_r($b);
exit;

为什么输出的是空数组?请帮忙改改
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