$redir = array("somewhere", "somewhere", "somewhere", "somewhere", "somewhere", "somewhere", "somewhere", "somewhere2", "somewhere2", "nowhere");
srand((double) microtime() * 1000000);
$page = $redir[rand(0, count($redir))];
header($page);
It works like basic mathematics. There are more of somewhere, so there's about a 70% chance somewhere will get picked randomly.