You don't really say it, but it sounds like you may want to do the avg based on ID, so what I would do would be:

my %procid;
my %procidcount;

open (FILE, "file");

while (<FILE>) {
   my ($id, $keystroke, $seconds) = split / /;
   $procid{"$id"} += $seconds;
   ($procidcount{"$id"})++
}

foreach my $ids (sort keys %procid) {
        printf "Average for $ids is %f...\n", $procid{"$ids"} / $proci
+dcount{"$ids"};
}
[download]

where data in file looks like this:

1234-5678 12 .345678
1234-5678 90 .123456
1234-5674 12 .345678
1234-5674 90 .123456
1234-5674 12 .345678
[download]

and output looks like:

Average for 1234-5674 is 0.271604...
Average for 1234-5678 is 0.234567...
[download]

-Waswas