mathematics in everyday life

[calimac]

Thanks to the local iteration of gasbuddy.com, I know that there's a pair of gas stations, right next to each other on the other side of the city, that have lower prices than any others in the area. When I'm in that part of town and need gas, I usually make a point of stopping there for my fillup.

But is it worthwhile to take the trouble to make a special trip? For that, I need calculations. First, I use my CD-ROM street atlas to determine how far it is, being careful to ensure it uses a believable route. Answer, 12 1/2 miles. That makes it a 25-mile round trip. Now, for the seat-of-the-pants rough calculations. My car gets somewhat better than 30 miles a gallon, and gas costs about $3 a gallon or a little more. So call it $2.50 worth of gas or a little less. That's how much I'd need to save per tankful to make it worthwhile (bearing in mind also that my time isn't worthless, nor is wear and tear on the car). The car holds ten gallons, so divide by ten and the price needs to be 25 cents a gallon less than I'd find it near home.

And it's close: right now it's 28 cents. But that's awfully marginal: taking my figures as hard I'd save a net 30 cents a fillup. Tempting as it looks it isn't worth the trouble from here, though it would be if I lived much closer. What is perhaps worthwhile is to buy smaller quantities of gas near home, figuring to increase the likelihood that I'll be low on fuel on the occasions that I happen to be near the gas stations in question.

Maybe I should have titled this "penny-pinching in everyday life."

Comments

[barondave.livejournal.com]

Hennepin Technical College was my longest commute. I taught in the evenings, so the drive back was without much traffic, most of which was highway. The temptation was always to go just a shade faster than the posted speed limit of 55 or 60 (depending on how close to the city you were). Okay, maybe a little faster than a shade. Anyway, I used to amuse myself my calculating how much time I'd save by going 65 vs. 55 over the seven or eight easy miles of the 15+ mile route, using cruise control. It worked out to a minute or two, so I usually just set the cruise control until the city traffic required a certain amount of weaving.

[whswhs.livejournal.com]

I do that kind of calculation for groceries. A round trip by bus costs $5; if the difference in price on the amount of groceries I can afford to get, or can manage to haul home by bus, doesn't come to at least that much, it's not a cash savings. Then there's the further calculation of time: if it takes me an extra half hour to make the round trip, that's an extra half hour's earnings foregone to do it. Of course, that actually works for me because my work is purely freelance; for someone on salary it wouldn't apply, or not as strongly.

[kalimac.livejournal.com]

I have never found my time to be quite so fungible as that.