this one put out by the city or this one which i find to be inferior but useful nontheless.
but here is the thing ... you need monedas or coins to ride the bus. no metrocards, no bills. only coins. easy enough, right? but if you need to ride the bus every day to and from work (and since i often have more than one student a day, that can be 4 or 6 colectivo rides) all of a sudden you need a hell of a lot of coinage.
apparently, there is a shortage of monedas here, so people at shops are reluctant to give you change unless absolutely necessary (even after you have bought something and asked them really nicely for coins).
in fact, several times when i have bought something and i was owed 5 or 10 centavos, instead of giving me a coin the cashier has given me a small piece of candy instead. yeah. wrap your mind around that. you are owed 10 centavos and instead of receiving money you just get a sucking candy. i wouldn't mind this, as i do like candy, but i also like being able to get to work. and much to my dismay, they do not accept candy as bus fare. (maybe they can create a little candy slot next to the coin slot? or you know how they used to have those big funnels at toll booths and you just threw your change in ... they could have those that accept change or candies)
anyway, now i am quite mathematic about my purchases, trying to get the most amount of change out of every item i buy. sometimes i will even spread out my shopping, going to more than one store so that i can receive more change per item.
i have realized that the problem is all due to the 2 peso bill. you see, there are coins for 5, 10, 25, 50 centavos, and a coin for 1 peso. then there are bills for 2, 5, 10, 20, 50, 100. it is this 2 peso bill which is ruining it for everyone.
for example ... you have a 5 peso bill and you buy something that is 3 pesos, but when you get change you get a 2 peso bill instead of getting 2 coins. so you have to be very thoughtful about what you are buying and how much you are giving the clerk, because if your change is in multiples of 2 then you'll never get any coins back. one also must consider that if you purposefully purchase something so that you will get 1.90 or 1.95 back, the most amount of change you could possibly receive in coins, it is possible that the store clerk may opt to round up and give you the 2 peso bill instead of monedas.
to be perfectly honest, it's more math than i care to do.
the solution to this problem is simple, although i am sure it will never be implemented. stop making 2 peso bills! instead make double the amount of 1 peso coins. another economic crisis solved by miss dewey d.