TestPrep #20, October 1996

16. Brown dwarfs—dim red stars that are too cool to burn hydrogen—are very similar in appearance to red dwarf stars, which are just hot enough to burn hydrogen. Stars, when first formed, contain substantial amounts of the element lithium. All stars but the coolest of the brown dwarfs are hot enough to destroy lithium completely by converting it to helium. Accordingly, any star found that contains no lithium is not one of these coolest brown dwarfs.

Breakdown analysis of stimulus:

Brown dwarfs:

-dim red stars

-too cool to burn hydrogen

-very similar in appearance to red dwarfs

Red Dwarfs:

-just hot enough to burn hydrogen

General Rules:

-Stars (including brown dwarfs and red dwarfs) contain substantial amounts of lithium when first formed.

-All stars except the coolest of brown dwarfs (which means that some brown dwarfs are included in the “all stars” group) are hot enough to destroy lithium completely by converting it to helium.

-Any star that contains no lithium is not one of these coolest brown dwarfs (taking  away the implicit double-negative which makes this tricky, rephrases into “Any star that contains lithium is one of the coolest brown dwarfs”)

The argument depends on assuming which one of the following?

(a)    None of the coolest brown dwarfs has ever been hot enough to destroy lithium.

(b)   Most stars that are too cool to burn hydrogen are too cool destroy lithium completely.

(c)    Brown dwarfs that are not hot enough to destroy lithium are hot enough to destroy lithium.

(d)   Most stars, when first formed, contain roughly the same percentage of lithium.

(e)    No stars are more similar in appearance to red dwarfs than are brown dwarfs.

Answer Choice Breakdown:

(a) Is the correct answer.

My original approach to this answer choice included arguing to myself that “Coolest brown dwarfs might be hot enough to destroy lithium, just not completely.”

Let’s look at the structure of the argument:

Conclusion (rephrased): Any star without lithium cannot be one of the coolest brown dwarf stars.

Premise #1: All stars, except the coolest brown dwarf stars, are hot enough to destroy lithium completely by converting it into helium.

After looking at premise #1, we see a more complicated relationship inherent in this answer choice than what it first appears:

If one can destroy lithium, then one can destroy it completely.

Implicit Assumptions:

Based on the last sentence, it is implied that the star always uses its ability to transform all its lithium into helium.

Looking at answer choice (a) again, if a Coolest Brown Dwarf has ever been hot enough to destroy lithium (and thereby, destroying it completely), the conclusion would prove to be false—a star completely without lithium COULD be a Coolest Brown Dwarf.

(b)   Most stars [that are too cool to burn hydrogen are too cool destroy lithium completely].

“Most stars” should automatically be a red flag. We are aware of two groups within the “star” category (red dwarfs, brown dwarfs), but we cannot make a judgment about a total population (most = =<51%) without more concrete knowledge.

Specifically, this question is discussing stars that are “too cool to burn hydrogen/too cool to destroy lithium completely” (coolest brown dwarfs). We cannot be sure if brown dwarfs are the only stars that are too cool to burn           hydrogen—it simply doesn’t say. It does say that only the coolest of the brown dwarfs are not hot enough to burn lithium completely – so this makes it clear that we are looking at just the sub-group of the coolest brown dwarfs.

Are these stars rare? Are they common? It doesn’t say. And because it doesn’t say the frequency of Coolest Brown Dwarfs, we can use our imagination:

CBD (rare) = 1% of star population

CBD (most) = 99% of star population

CBD (minority) = 49% of star population

CBD (majority) = 51% of star population

Since it could go either way, this answer choice must be thrown out.

(c)    Brown dwarfs that are not hot enough to destroy lithium are not hot enough to destroy helium.

This answer doesn’t seem to be as tempting as (b). The passage doesn’t mention anything about destroying helium (it mentions converting lithium INTO helium), and the assumption (and therefore right answer) should be addressing destroying lithium (see Conclusion/Premise).

(d)   Most stars, when first formed, contain roughly the same percentage of lithium.

The passage itself states that all stars, when first formed, contain a substantial percentage of lithium. So, although this could be true (it could also be equally false), it is not necessary to base the conclusion on this fact. Especially, if you look at the implicit assumption (that given the ability, it will transform all its lithium into helium), the percentage of lithium it first contains does not matter.

(e)    No stars are more similar in appearance to red dwarfs than are brown dwarfs.

This answer choice rewards your tired eyes after working through the other answers. Arguably this is the most “obvious” wrong choice. As stated earlier, we are only presented with two classes of stars (red dwarfs, brown dwarfs), so we cannot make assumptions based on the entire star population—and certainly not an absolute statement (“no stars….”) such as this. In addition, appearance—though mentioned—is not the heart of the issue. The focus of the argument is function (especially of our precious Coolest Brown Stars).

I think it also helps if you picture “The Fonz” as the Coolest Star. Or not.

Happy Studying!

I am not affiliated with Powerscore (or Amazon…for that matter) in any way, but this book has helped me immeasurably in my studies. In untimed tests, I used to miss about 14 questions per LR section (yikes!), and in three months, I’ve narrowed that down to about 5 questions a section — with three months of studying left to go.

If $64.99 is too expensive for a college budget (it certainly was for me), you might want to check craigslist for used, clean copies. I have purchased most of my prep materials for the LSAT at half the retail price.

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That being said, I have found a couple things in my journey:

1. The Logical Reasoning section is pretty “easy” up until about question 15.

2. From around question 16-20 (ish), it is ridiculously difficult.

3. 20 – 25, 26, 27 – gradually gets easier (probably on the same level as the #11-15 questions).

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The testmakers make you feel comfortable at first, and then try to frustrate you by throwing in hard questions when you don’t expect it (or at least, you used to not expect it). And a series of difficult questions frustrates the test-taker (me), resulting in broken concentration, broken spirit, and inevitably wrong answers.

1. The best way to combat this (and this is incredibly time-effective) is to focus on the first 10 questions pretty rapidly – these are mostly from these categories:

-Must be true

-Basic assumption

-Weaken

-Point at Issue

—> Very easy things that anyone who studies the Powerscore materials would feel very comfortable with, raising confidence, and you’re pretty free of the mental baggage of  “I wonder if the answer I picked is really the best answer…” that can distract you from giving the rest of the test your full attention.

If you can get through the first 10 questions in 10 minutes (accurately and effectively), you’re well on your way to setting yourself up for success on the LSAT.

2. Spend a little extra time on questions 11-15, as they get a little more difficult. There is an increase in focusing on “structure” of the argument, rather than the words used in the argument (which is what 1-10 generally seems to do). Because of this, expect to see these types of questions:

-flaw in the argument

-assumption

-logical completions/function questions

-principle questions

Clearly, the words used are a key in determining the right answer, but also the relationship between premises, counter-examples, and conclusions are increasingly more important.

3. #16-20(ish) seems to be the hardest problems in LR sections across the board. These problems generally include question types:

-Pattern of Reasoning

-Flaw of Reasoning

-Error of Reasoning

-Must be True (using Informal Logic, and more complex conditional clauses)

-Percentage / Population

-Parallel the Argument

These questions might involve diagramming — not only the original argument, but each answer choice — which is a huge investment of time.

Your best bet is simply to save these questions for last. This is beneficial in the following ways:

1. You won’t waste time on one particular question, as you would’ve finished about 25-30 questions by this point.

2. You won’t be distracted by other questions and possible “right answers” lingering in your mind, as you can be certain that you’ve finished all the easier questions.

3. You won’t fall into the trap the test-makers anticipate – being bombarded with difficult questions until it makes you breakdown and cry for mercy.

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Practice, Practice, Practice. Incorporate this format into your studying – Tackling #1-15 first, skipping to the last problem, and working your way backwards. Make sure you practice with the official answer sheet so you “bubble” the right answers on your page.

Hopefully, this will work as well for you as it did for me!

Happy Studying!

If you don’t know already, the LSAT stands for the Law School Admission Test and it is administered four times a year (June, September/October, December, and February). For chances at early admission to law school, you must take the LSAT by September (in the year which you are applying). The best thing about the LSAT is that it is a highly learnable test. The questions, though demanding because of time restrictions, are very predictable.

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The format of the test is as follows (allowing 35 minutes for each section, multiple-choice format):

Logical Reasoning (2 sections, anywhere between 24-27 questions per section, approx. 50% of your total score)

Analytical Reasoning (fondly known as the “Logic Games” section, anywhere between 24-27 questions, approx. 25% of your total score)

Reading Comprehension (anywhere between 24-27 questions, approx. 25% of your total score).

Experimental Section – On test day, you will receive an extra section that isn’t present in TestPrep materials – the experimental section. It could be chosen from any of the three above categories, and there is simply NO WAY to know which section is experimental. You must try to do the best you can on all sections. It is important to practice with an extra section when you get to timed practice tests, to help combat test fatigue (more on this in a later post).

Writing Section – You will be given 35 minutes to write an argumentative essay from the prompts given. Most law schools seem to understand that after 2.5 hours of test-taking, this essay is not the best medium for showcasing an applicant’s abilities. However, failure to write anything down will result in an incomplete LSAT and you will not receive your score. Since you have to be there, you might as well try and it isn’t as hard as you think (a clear and simple 5 paragraph structure will suffice).

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Obviously, to complete 24-27 multiple-choice questions in 35 minutes (a little less than 2 minutes a question), you MUST have a solid understanding of how the test makers think, what traps they are trying to lure you into, and a good idea of what the answer *should* be–before you start reading the answer choices (with the exception of certain questions from the Analytical Reasoning/Logic Games section).

I have been told that the Logic Games/Analytical Reasoning section is the easiest to improve (indeed, from first hand experience I agree), and the Reading Comprehension section is the most difficult (more on this later).

Since most of your score relies on your Logical Reasoning (LR) score, spend a lot of time on this section. Period. I am working my way through this as well, and will be posting more of my escapades/insights on here shortly. My goal is to understand how the test-makers think — and I hope you will join me.

For more about the LSAT, I suggest starting from the source itself (the Official LSAC website):

http://www.lsac.org/LSAT/about-the-lsat.asp

As always, please leave me feedback of what you think would be helpful, what you need help on, a question you don’t understand, et cetera. I’ve gone through a lot of PrepTests and will help as much as I can.

Happy Studying!