Results:
$students = [
'Иванов' => ['Математика' => 30, 'Русский' => 30, 'Информатика' => 50],
'Петров' => ['Математика' => 50, 'Русский' => 40, 'Информатика' => 30],
'Сидоров' => ['Математика' => 30, 'Русский' => 50, 'Информатика' => 40],
];
$averageScores = [];
foreach ($students as $student => $scores) {
$averageScore = array_sum($scores) / count($scores);
$averageScores[$student] = $averageScore;
}
arsort($averageScores);
foreach ($averageScores as $student => $averageScore) {
echo $student . ': ' . $averageScore . "\n";
}