thank you!! 
#!/usr/bin/perl -w

use strict;

my %grades;

while (<DATA>) {
     chomp;
     my($student,$grade) = split (" ",$_);
     $grades{$student} .= $grade . " ";
     #$grades{$student} = $grade;
     print "\$grades{$student} is $grades{$student}\n";
      
}

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

__END__
lee  90
lee  100
kim  90
kim  90




./././perl.score
$grades{lee} is 90 
$grades{lee} is 90 100 
$grades{kim} is 90 
$grades{kim} is 90 90 
kim: 90 90      Average: 90
lee: 90 100     Average: 95


so 
$grades{$student} .= $grade . " "; is more like

$grades

[download]
I also tried this for just education.(which btw is not the same solution and answer). 
#!/usr/bin/perl -w

use strict;
use diagnostics;

my %grades;
my %student_n;

while (<DATA>) {
     chomp;
     my($student,$grade) = split (" ",$_);
     $grades{$student} += $grade;
     $student_n{$student}++;
}

for (sort keys %grades) {
    my $avg = $grades{$_} / $student_n{$_};
    print "$_ average of $student_n{$_} exams are $avg\n";
}

__END__
lee  90
lee  100
kim  90
kim  90
~

./././././perl.score_copy
kim average of 2 exams are 90
lee average of 2 exams are 95

[download]

In reply to Re^2: first perl example from perl book by convenientstore
in thread first perl example from perl book by convenientstore

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