Money's got tight, every penny I can save is important.
With gas prices rising the way they are, I have a couple of ideas on how
to save as much money as I can on gas, but I'm not sure how to prove or
disprove it mathematically.
I know there's some people around here who are better at math than I am.
I'd appreciate it if the engineering-scientific types would look at what
I'm thinking to see if it makes sense.
Here's the deal. I average around 31 mpg in my car. That gives me about
$0.10/mile cost for gas at current local gas prices. It was $0.08/mile
last year.
Currently, gas prices in the area are around $3.55/gal for 87 regular
... except for one station that's currently at $3.35/gal. I'll get to
that a bit later.
My style of driving has been to empty the tank before filling up. That
gives me an average range of around 400 miles and 12 gallons per fill up.
Part I - I'm considering changing my style in order to minimize the
effects of rising gas costs.
I figure that when gas prices are rising, it makes more sense to top off
the tank nearly every day, so that the tank is always nearly full at the
lower price (i.e. before the price gets raised again).
The incremental change in the cost of the gas will be less than the
change from waiting till the tank is empty. The aggregate cost for a
given volume of gas should be less if you buy gas more frequently when
prices are rising, and if you run the tank all the way out before
filling up when prices are falling. shouldn't it?
Or am I missing something obvious?
Part II - I will be making approximately a daily 60 mile round trip
commute, 7 days a week for the next 8 weeks, with a 120 mile round trip
M-F for the following 5 weeks - my internship & radiation therapy overlap.
The location where I will be doing my internship is only 4 miles from
the hospital, so I can't make any significant savings by dropping out of
school until the radiation therapy is complete. I'd only save the cost
of 2 gallons of gas per week.
Plus I'd still only be deferring the cost of commuting to the internship
until a later date when gas prices will probably be higher still.
With my gas mileage at around 31 mpg, I burn not quite 2 gallons in 60
miles; not quite 4 gallons in 120 miles. The cost per mile for gas is
averaging about $0.10 per mile at today's prices.
There is a single station in my area that has gas for $0.20/gallon less
than any other station. Part of a chain, but its prices have been
consistently that much lower for over a year. I pass it on the way
between my home in Raleigh, and my apartment down here at school. I've
been filling up there, and that $0.10/mile cost if figured on that cost.
But it's a bit out of the way for the commute to my internship.
Ignoring the time involved ...
How many miles out of my way does it make sense for me to drive - miles
added to the commute - to get my gas from that station selling gas at
$0.20/gallon less?.
I have a good idea how many gallons I'm going to need every day of the
commute. If I divide the savings per sale ($0.20 for 1 gal, $0.40 for 2
gal, ...) by my cost per mile ($0.11), does that give me the correct
number of miles I can afford to detour before the cost of the detour
exceeds the savings?
Does ...
"((Total Savings on the sale/cost per mile = number of miles)*0.9)"
... work to give me the number of miles I can drive without burning up
the savings?
I'm figuring I can afford to detour about 3.25 miles for 2 gallons, 6.55
miles for 4 gallons ... up to 19.64 miles for 12 gallons.
Does that look right?
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