January 07, 2005
 

Optimizing spending on petrol

As a followup to last month's rant on the way petrol is priced, I started wondering about how much quantity I should fill to ensure that I do not fork out any extra money and in fact the petrol pump dealer instead ends up paying the deficit. Through some trial and error, I hit upon the fact that currently, when petrol costs Rs. 44.21 per litre in Bangalore, I stand to gain 5 paise when I fill 3.1 litres since it would work out to Rs. 137.05. But really I'm never going to pay that .05 bit and neither does the dealer ask for it.

So when I do it continously enough, I'm bound to recover my earlier losses (after a lot of petrol filling!). But the price of petrol is never going to be Rs. 44.21 forever. So I wrote some simple Perl code which lists out the quantity of petrol I need to fill to gain in the deal, assuming that the dealer doesnt bother about a deficit of upto 10 paise. Feel free to change the location of your Perl interpreter in the first line.

#!/usr/local/bin/perl -w

use Getopt::Long;
use POSIX;

my $usage="Usage: ".__FILE__." -rate [petrol price per litre] -maximum [amt. of money]\n";

my ($rate,$maximum);

GetOptions("rate|r=f" => \$rate,"maximum|m=i" => \$maximum);

die $usage if (! defined $rate || ! defined $maximum);

my $minpetrol=1;

print "Money limit (max): $maximum\n";
print "Petrol limit (min): $minpetrol\n";
print "\n";
print "Petrol\tAmount\tPotential Gain\n";
for(my $i=$minpetrol;;$i=sprintf("%.1f",($i+.1)))
{
my $totalamt=sprintf("%2.2f",$i*$rate);
my $flooramt=floor($totalamt);
my $diff=sprintf("%.2f",($totalamt-$flooramt));

last if ($totalamt > $maximum);
print "$i\t$totalamt";
print "\t$diff" if ($diff > 0 && $diff <= .1);
print "\n";
}


Labels: petrol