$ perl -Mstrict -Mwarnings -E '
my $rsSum = \ do { my $dummy };
my $rsAvg = \ do { my $dummy };

sub sum (@)
{
    ${ $rsSum } += $_ for @_;
    &avg;
}

sub avg (@)
{
    ${ $rsAvg } = ${ $rsSum } / scalar @_;
}

sum( 3, 4, 5, 6, 7 );
say qq{Sum - ${ $rsSum }\nAvg - ${ $rsAvg }};'
Sum - 25
Avg - 5
$

##</code><code>##

$ perl -Mstrict -Mwarnings -E '
my $rsSum = \ do { my $dummy };
my $rsAvg = \ do { my $dummy };

sub avg (@)
{
    &sum;                    
    ${ $rsAvg } = ${ $rsSum } / scalar @_;
}

sub sum (@)
{
    ${ $rsSum } += $_ for @_;
}

avg( 3, 4, 5, 6, 7 );
say qq{Sum - ${ $rsSum }\nAvg - ${ $rsAvg }};'
Sum - 25
Avg - 5
$