php实现中奖概率

同事说的一道面试题

function r($data){
	$n = rand(0,100);
	$temp = 0;
	foreach ($data as $k => $v) {
		$temp+=$v;
		if($n<=$temp)
		{
			return $k;
		}
	}
	return false;
}
$r = r(["t"=>0.1,"1"=>0.5,"2"=>1.5,"3"=>10,"4"=>20]);
 echo $r==false?"未中奖":$r."等奖";