New York's New Subway Math

The NYT has a good article this morning on the "new subway math" - the way in which anybody refilling their MetroCard is going to have to do some rather recondite calculations in order to ensure they don't end up with random nickels and dimes they can't spend on transportation.

But the cut-out-and-keep graphic alongside the article ("Save This Chart", it's headlined) is pretty useless. As of March 2, it says, if you spend $15.65 on a card you'll end up with a nice round $18; if you spend $24.35 you'll end up with $28; and so on.

Never mind that March 2 is so far away that only the most anal NYT readers will manage to keep the graphic until then. The problem is that whoever put this chart together forgot the whole point of it: it's meant to be designed for people who are refilling their MetroCards - cards which are likely to have some amount of money on them which is not divisible by $2, perhaps because they were used on the PATH or the AirTrain. If the amount on your card is divisible by $2, you don't really have a problem: you can just swipe it all the way to $0 and/or get one of the standard preset refills.

Much more useful would be a chart which told you how much to put on your card in order to ensure the 15% bonus and get an odd amount of money added. For instance, you have a spare $1 on your card: what should you do?

The answer is that you should add $11.30, which with bonus becomes $13, or else - easier to remember - add $20, which with bonus becomes $23. When you add those sums to the $1 on your card, you have a MetroCard whose balance, once again, is divisible by $2.

The NYT mentions with approval Steven O'Neill's online MetroCard bonus calculator, but idiotically doesn't link to it - here's the link, which is much more worth saving than anything in the newspaper. On the other hand, if you're looking for an insanely anal and largely obsolete five-year-old guide to MetroCards, written when they were still in their infancy and subway tokens were still accepted, you could try going here.