When I was about twelve or thirteen years old, I read Douglas Adams's Hitchhiker Trilogy, as one does at that age. In Life, the Universe, and Everything, Adams describes a space ship that is powered by bistromathics. The short version of how it works is that there is an artificial restaurant with seating for twelve, and robots sit there arguing over the bill and who owes what.
This was certainly an amusing idea to me at the time, but I did not understand at the time how much this joke was based in reality until I was about 25 years old, and went out to eat with several of my friends where we were splitting the bill. Our group was small enough to figure out what each of us had to pay initially, and calculating the tip was not a big deal, but then there was the problem of people paying an amount that was close enough to what they owed to be satisfactory. Suppose that Joe only has a $20 bill, but after tip, he owes $15, so does anyone have a five for change? Now picture at least half the people at the table doing this. We tossed around money until we had a reasonable amount in a pile in the middle of the table, and nobody protested about putting in too much. Presumably, however much anyone overpaid, they were okay with this.
This is why some people who eat out regularly together (say, co-workers going out to lunch) will agree to take turns paying the whole bill. The only complicated thing about this is remembering whose turn it is, which gets increasingly difficult the more people are in your group, but is completely manageable if one keeps a record of it in a day planner. Also, anyone who is clearly trying to make everyone else pay for expensive items will eventually have their turn to pay come around, and while they may order a garden salad for themselves everyone else will be ordering steaks.
This is also why the $20 bill is sometimes called the "yuppie food stamp." If you're eating out, and splitting the bill, you need some cash. If you don't usually carry cash, the easiest way to get it is to go to the ATM, and that means everyone in the restaurant is going to pull out $20 bills to pay for the meal. Yes, they can certainly be used to pay for the meal, but they are by no means convenient. Hence, "yuppie food stamps." (And, while on the subject, why can't our ATMs have multiple denominations of currency? Of all the things Europe does that we don't, this seems like it would be the easiest to change.)
Given all of this madness, it's hard for me to wrap my head around the idea that 80-year-olds could be good at splitting the bill. Is it because they eat at places where they pay less for the food? Because they carry more than just $20 bills? Because they just care less about paying exactly what they owe? We may never know, because we are all the way in panel six when T-Rex tells us about this. Why won't you tell us the secret, T-Rex? Why do you insist on telling us only their collective term?