# how to calculate the winning special offer

This is surely way below the level of maths questions you normally get on here but please humor me!

I have written a simple app that compares beer offers and works out the best (cheapest) price per 100ml. It works it out using the calculation written below:

function getPricePer100ml(cansize, cansinpack, numberofpacks, cost) {
var totalCans = cansinpack * numberofpacks;
var totalMl = totalCans * cansize;
var total100Mls = totalMl / 100;
return cost / total100Mls;
}


I run this twice to get each offers price per 100ml and then the lowest price "wins".

The issue I am having is understanding what I need to do on top of this to factor in the ABV (strength) of the beer. This is in % so for example:

offer1per100ml = 0.65p - 3.8%ABV
offer2per100ml = 0.75p - 5.2%ABV


My app would class offer 1 as the winner because its cheaper per 100ml but I suspect that you get more bang for your buck by paying the extra 10p and buying the strong stuff.

How can I write this mathematically? Or am I approaching this wrong?