#!/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