確率について質問です

$foo=array(
"A" => 60,
"B" => 20,
"C" => 10,
"D" => 7,
"E" => 3,
);
$r = rand(1, 100);
foreach($foo as $k => $v){
if($r<=$v){
$ans=$k;
break;
}
$r-=$v;
}
echo $ans;