We don't need to assume anything. We have 8 bottles, so each of us drank 8/3.
John gave 5 and drank 8/3, so 7/3 is the difference
Bill gave 3 and drank 8/3, so 1/3 is the difference.
So, they should divide the money in proportion 7:1


>If we assume 1$ a beer. If it is !.50 a beer, then you didn't pay enough. Hence the x in my answer.
>
>>>>John brought 5 bottles of beer, Bill brought 3 bottles, when I came. So, we drank this beer together and then I gave them $8 (all I had at this moment). How should they divide this sum?
>>>
>>>$7 for John, / $1 for Bill.
>>
>>And * for you :)