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 All content © Seung Lee slee [at] lagomorpho.com
 Math Is Hard Tue, Apr 07 2009 00:21

I had a little dilemma on my way to work tonight. My monthly metrocard had run out. Luckily, I had next month's already in my wallet. The problem is that I will be going out of town for about a week starting next week.

I had the choice of either using the monthly card I already had or purchasing a 1-week card and push back on using that monthly card. Here are some numbers:

30-day card: \$81
7-day card: \$25

30-day card: \$81/30 = \$2.70 per day
7-day card: \$25/7 = \$3.57 per day

My first instinct says that since I'd be gone for a week, it would cost me \$18.90 for the loss of the week on the 30-day card whereas the 7-day card would cost me \$25. The advantage to using the 7-day card though would be pushing back the day I use the 30-day card for 2 extra weeks. That might some day pay off by me having an extra 30-day card, maybe.

The train was coming into the station so I just used the 30-day card I had.