Tag Archives: consumption

Can a Hybrid Save Me Money ?


Since the oil demanded from Europe is low, gas prices across the nation about about to drop below $2 per gallon by February since 2009. However, this decrease in gas price does not necessarily mean we are saving as much money as we possible can.

Take a regular compact car as an example; the 2014 Toyota Yaris gets approximately 32 MPG in cities, with a 16-gallon gas tank. If a person drives spends most of his time driving in the cities, assuming that the gas price is 2 dollars per gallon, with a full tank he can drive

16 gal x 32 miles / gal = 512 miles

with the a cost of

$ 2 / gal x 16 gal = $32.

However, a person who owns a hybrid, a 2014 Toyota Prius for example, with 50MPG in cities and 16-gallo gas tank, can drive

12 gal x 50 miles / gal = 600 miles

with the same cost of the Yaris’ .

From another perspective, Hybrid cars also do less harm to the environment than do conventional cars. A conventional compact sedan emits about 87 pounds of CO2 while a hybrid electric car only emits 57 pounds of CO2.

It is because of the fuel economy that an environmental friendly car can deliver that the latest Consumer Reports has concluded that about 39 percent are considering buying a hybrid for their next car. Even though a hybrid car usually costs about 3000 to 4000 dollars more than a regular car, not only will owning a hybrid benefit the consumer, but it will also be favorable to the environment.



source 1 

source 2 


Sample Post: The Usage of Paper Towels

A friend of mine recently told me about a TED video on how to dry your hands with a single paper towel. The speaker, Joe Smith, presents some compelling numbers. He states that 13 billion (that’s \(13 \times 10^9\)) pounds of paper towels are used in the United States every year. He further suggests that if we restrict ourselves to using 1 sheet of paper towels every time we dry our hands, we could save 571,320,000 pounds of paper towels.

Certainly this figure sounds impressive! 500+ million pounds of paper towels is hard for me to even imagine. The problem is that whenever we consider the entire population of the United States, we will always get a large number. For example, if everyone drank 7 cups of water a day instead of the recommended 8, we could save \[ \frac{ 1 \text{ cup of water }}{\text{ 1 person, 1 day }} \times \frac{3 \times 10^8 \text{ people }}{ \text{ the US}} \times \frac{365 \text{ days }}{1 \text{ year }} \approx 9 \times 10^{10} \text{ cups per year in the US }\] or 90 trillion cups of water a year!  I’m not writing this to argue that we should drink less water. I’m simply saying that we can make impressive numbers by using large scales, like the population of the US, and long periods of time, like a year.

The figures in the TED talk are the same way. They are giving us a figure that happens in a large scale over a long period of time. So how can we determine if this is something we should actually focus on? Assuming we believe Smith’s oddly precise figure of 571,320,000 pounds of paper towels, let’s calculate the percentage saving on overall paper towel consumption.

\[\frac{5.71 \times 10^8}{13 \times 10^9} \times 100\% \approx 4\% \]

While 4% is not a lot, I think it’s big enough to warrant my attention (others may disagree on this). I still have two concerns, though:

  1. Is it a good trade-off? Shaking your hands, which spreads water, may also spread disease.
  2. Is this the right figure to look at? How does reducing the usage of paper towels this way compare with our usage of paper products in general?

We can’t really address the first one with the math we’ve learned so far. I did find this article, which suggests that paper towel usage is more hygienic than air dryers.  It argues that airborne bacteria laden droplets may be a reason paper towels are superior to hand dryers. If so, Smith’s drying method, which requires “shaking,” may mitigate the advantages of using paper towels. We can only speculate about this, though.

We can, however, address the second problem. According to the EPA, the US uses 69 million tons of paper and paper board products each year. Smith’s method of drying, according to his numbers, we’d save \( 5.71 \times 10^8\) pounds of paper towels. Let’s convert that to tons: \[ 5.71 \times 10^8 \text{ pounds of paper towels } \times \frac{ 1 \text{ ton }}{ 2,000 \text{ pound }} \approx 2.86 \times 10^5 \text{ tons of paper towels }\] or 286,000 tons. Compared with 69 million tons, that seems very small to me. Let’s find out the percent of paper saved from this method compared with the total amount of paper consumed: \[\frac{2\times10^5}{6.9 \times 10^7} \approx 0.4\%\] The percentage is  in fact very small.

While I think it’s very important to save paper products, I’m not sure this is the best way to do it. The savings seems small to me and, if this technique is less hygienic, then we may end up wasting more to deal with illness.

I think a better way to save paper products might be to switch to digital readers, but I am not sure. For my next post, I might try to figure out how much I save in paper by using my kindle and compare it with the energy required to make and use it.