my %hash = (
  dog    => 5,
  sheep  => 10,
  cat    => 3,
);

my %hash2 = (
  dog    => 11,
  budgie => 1,
  cat    => 4,
);

print "$_: ", $hash{$_} * $hash2{$_}, "\n"
  for grep exists $hash2{$_}, keys %hash;

__output__

cat = 12
dog = 55
[download]

Be careful not to stringify your numeric values or you could get unexpected results.
HTH

_________
broquaint