<?php
$arraynumber = [1, 2, 5,];
function tosplit($arraynumber)
{
    $array = array();
    for ($i = 0; $i < count($arraynumber); $i++) {

        $array[$i] = ($arraynumber[$i] / 2);
    }
    return array($array);
}
var_dump(tosplit($arraynumber));