weighted_random.php

<?php

$items = array(
'original' => 50,
'v1' => 20,
'v2' => 10,
'v3' => 20,
);

$rand = rand(0,100);
$sum = 0;

foreach($items as $id => $item){

   $sum += $item;
   if($rand <= $sum){
       echo "$id => $item  \n";
       break;
   }

}