#!/usr/bin/perl
###########################################
# mpgal - miles/gallon => liters/100km
# Mike Schilli, 2004 (m@perlmeister.com)
###########################################
use warnings;
use strict;

use Math::Algebra::Symbols;

my ($gallons, $miles) = 
   symbols(qw(gallons miles));

my $liters = $gallons * 37854118/10000000;
my $kilometers = $miles * 1609344/1000000;
my $usage = $liters / $kilometers * 100;

print "Formula: $usage\n";

for $miles (qw(20 30 40)) {

    $gallons = 1;

    printf "$miles m/gal: " .
           "%4.1f l/100km\n", eval $usage;
}