Let’s return to our original prompt and attempt to identify the main components.
Many citizens of Lakota are experiencing rising costs of electricity. A recent study of household electric costs in Lakota found that families who heated their houses with free-standing heating fans alone spent more on electricity than did families using central heating systems alone for heating. However, those households that reported using both heating fans and heating systems spent less on electricity than those households that used either heating fans or heating systems alone. Thus, the citizens of Lakota should follow the study’s recommendation and use both heating fans and central heating systems in order to save money on electricity.
First, we always want to identify the conclusion. What is it that the author wants us to believe or what course of action is he recommending? It should be fairly obvious. His conclusion comes at the end of the paragraph: “Thus the citizens of Lakota should follow the study’s recommendation and use both heating fans and central heating systems in order to save money on electricity.” A word like “Thus” or “Therefore” nearly always indicates a conclusion. And the verb “should” nearly always indicates a conclusion, as it indicates something that the author wants us to believe or do. So be on the lookout for word cues if you are having trouble identifying the conclusion.
Now, what evidence does the author use to support his conclusion? Basically, the remainder of the paragraph. He states that many citizens of Lakota are experiencing rising costs of electricity, and then he cites the study indicating that those who heated their houses with free-standing heating fans alone spent more on electricity than those who used central heating systems. And those that used both spent less than those who used one or the other. So this is the evidence he uses for his argument.
Now what are the things the author assumes to be true?
For one, he assumes that the sample population in the study is representative of all of Lakota. The study may have been sampled from only one subset of the population in one geographical area, and thus may not be representative of the whole. The study may have sampled an older part of town, in which the population owned old, inefficient heating fans, which would affect their ability to heat a home. Furthermore, the study looked at “families” household electric costs. We are not told what constitutes a “family” and whether or not it includes single citizens of Lakota.
Second, the author assumes that heating is the biggest factor in electricity usage. What about electricity used for refrigeration and lighting of homes? He gives no data to suppose that heating costs would trump other electricity costs and therefore be a high priority for Lakota citizens. Furthermore, what if heating is only needed 2 months out of the year? The author does not give an indication as to how often the citizens of Lakota need to have their homes heated.
Third, the author assumes, even if heating were the highest electricity cost, that using both heating fans and central heating systems would save an appreciable amount of money. Perhaps the problem lies elsewhere– like in the insulation in the citizens homes. Heating of a house is affected by poor or inconsistent insulation. Perhaps proper insulation would save more money on electricity than using both either heating apparatuses, and would cost less to purchase. The author does not seem to take into account other ways for reducing heat-related electricity costs.
We could also mention the fact that the evidence offered gives no indication as to the position and placement of the free standing heating fans. An improper placement of these fans (like pointing them towards a window) might lead to inefficient heating, while proper placement of the fans would encourage more efficient heating, and thus, lower costs. Similar things could be said with regard to variables such as home-wide fenestration and the electrical conductivity of the heating appliances.The author overlooks possibilities like these in his recommendation to the citizens of Lakota.
Now, these are just a few of the assumptions in this argument. We could probably identify more, but these are some of the things that the author of this argument assumed to be true in order for his argument to be sound.
Identifying assumptions is the most important skill to learn for this GRE question type.