Accumulate the data as you read in the file:

use warnings;
use strict;

my %r;
while (<DATA>) {
    chomp;
    my ($k, $s) = split;
    $r{$k}{count}++;
    $r{$k}{sum} += $s;
}

for my $key (sort keys %r) {
    print "$key\t$r{$key}{count}\t", ($r{$key}{sum}/$r{$key}{count}), 
+"\n";
}

__DATA__
1    196
1    190
1    200
2    20
3    25
3    19
3    39
4    40
4    41
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