my $last;
my $sum;
my $count;
local $, = "\t";
local $\ = "\n";
while (<>) {
    chomp;
    my ($k, $v) = split /\t/;
    if (defined($last) && $k ne $last) {
        print $last, $count, $sum/$count;
        ($last, $count, $sum) = ($k, 0, 0);
    }
    $count++
    $sum += $v;
}

if (defined($last)) {
    print $last, $sum/$count;
}