<?php

error_reporting(-1);
mb_internal_encoding('UTF-8');

$pupils = 30;
$rhyme = 5;
$presentPupils = range(1, $pupils);

for ($i = 1; count($presentPupils) >= $rhyme; ) {
    foreach ($presentPupils as $key => $value) {
        if ($i == $rhyme) {
            unset($presentPupils[$key]);
            $i = 1;
            continue;
        }
        $i++;
    }
}
$winners = implode(', ', $presentPupils);
echo "Выигрышные места: $winners.";