Math Is Hard
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.