x = c(S) = Count(S)
y = m(S) = Min(S[0]/A, S[1]/A, ..., S[n]/A)

$x = count($s);
$y = min($s) / (array_sum($s) / count($s));

function avg($values) {
    $values = is_array($values) ? $values : func_get_args();
    return array_sum($values) / count($values);
}

$x = count($s);
$y = min($s) / avg($s);

$values = [];
$p = [1, 5, 3, 6, 4];

for ($i = 1; $i <= count($p); $i++) {
    $s = array_slice($p, 0, $i);

    $x = count($s);
    $y = min($s) / avg($s);

    $values[] = compact('x', 'y');
}

print_r($values);