open my $fh, '<', 'grades' or die "Can't open grades: $!\n";
while (my $line = <$fh>) {
    my ($student, $grade) = split ' ', $line;
    $grades{$student} .= $grade . ' ';
}

foreach my $student (sort keys %grades) {
    my ($scores, $total) = (0, 0);    
    my @grades = split ' ', $grades{$student};
    foreach my $grade (@grades) {
        $total += $grade;
        $scores++;
    }
    my $average = $total / $scores;
    print "$student: $grades{$student}\tAverage: $average\n";
}