5 Hardest LSAT Logical Reasoning Questions

Today, I'll show you how to approach 5 difficult LSAT Logical Reasoning questions. Students ask me to explain these questions all the time, so I'm using this week's main post to do so. I'm not posting the actual questions because I don't want to get a visit from the folks at LSAC (although I'm sure they're wonderful people). Here's where to get the actual LSAT PrepTests.

Also, here are some other Difficult LSAT Logical Reasoning Questions.

1. Reproductive abnormalities in fish and whether or not they're caused by dioxin (PrepTest 45 - December 2004 LSAT, Section 1, Question 12)
Evidence: Even after a mill shut-down, dioxin decomposes slowly. During shutdowns, fish hormone levels quickly return to normal levels.

Conclusion: Dioxin probably isn't the cause of abnormalities.

Question stem: "Which one of the following statements, if true, most seriously weakens the argument?"

Explanation:
If normal river currents move dioxin far downstream in only a few hours, then the fish should be in clean water. It wouldn't matter whether the dioxin decomposed or not because it already left the area.

Wrong answer choices:
A - Weakens it a little bit, but not enough.
B - Irrelevant. The rate of dioxin decomposition doesn't matter.
D - Refers to physiological, not reproductive, so it's too broad.
E - Too broad AND irrelevant.

The correct answer is C.


2. PrepTest 38 (October 2002 LSAT), Section 4, Question 16 - page 346 in Next 10
(the question discusses: people, distrust, confident, abilities, challenge)

Evidence group: People who do not believe that others distrust them
Conclusion group: People who tend to trust others

Question Stem: "The conclusion above follows logically if which one of the following is assumed?"

This is a sufficient assumption question.


After identifying each piece of the stimulus, we can arrange them like this:

Evidence: Not Believe Others Distrust ---> Confident ---> Difficult Task as Challenge
Conclusion: Tend to Trust Others ---> Difficult Task as Challenge

We could diagram this as:

Evidence: NOT BOD ---> C ---> DTC
Conclusion: TTO ---> C ---> DTC

The necessary condition (regarding/thinking about each difficult task as a challenge rather than as a threat) is the same for both. Why? Because the final clause ("since this is precisely how...") supports the part of the conclusion that states "think of a difficult task as a challenge..." Since we know that "Difficult Task as Challenge" is a necessary result of "Confidence," we can put DTC after C in the evidence.

The cleanest way to close the gap is to say everyone in the conclusion's group of people ("people who tend to trust others" = "TTO" ) falls within the evidence's group of people ("people who did not believe that others distrust them" = "NOT BOD").

Choice C says this word for word.

The key is in noticing the evidence group and conclusion group are really discussing two different groups of people, and we don't know anything about how they relate to each other.

As always, try not to get overly involved with (or scared by) the topic of the argument. Instead, focus on its structure.


3. Rattlesnake's age determined from # of sections in its rattle (PrepTest 30 - December 1999 LSAT, Section 2, Question 22 - page 60 in Next 10)
Evidence 1: If rattles were not so brittle
Evidence 2: A new section of rattle forms whenever rattlesnakes molt

Conclusion: One could determine rattlesnake age by # of sections in rattle.

Question stem: Which one of the following is an assumption the argument requires in order for its conclusion to be properly drawn?

Explanation: We're looking for something that "must be true" in order for the argument to work. Therefore, if we negate each answer choice, we'll find the correct answer choice by seeing which one, when negated, causes the argument to fall apart.

A. This answer choice is sufficient for the argument to work, but it doesn't have to be true for the argument to work. The length of the interval doesn't matter as long as there is regularity to the molting rate.
B. This answer choice is irrelevant. We don't care what the rattles look like.
C. This negation strengthens the argument. In its original form, it weakens the argument.
D. We don't care about brittleness' relationship with lifespan.
E. This negation destroys the argument. We need rattlesnakes to molt at regular, predictable rates if we are to determine a rattlesnake's age by the number of sections in its rattle alone.

E is correct because it eliminates the possibility that food availability alters the rate at which rattlesnakes molt.

Also see: Necessary Assumption Question: The Rattlesnake Folktale


4. Beethoven Mercury Venereal Disease (PrepTest 28 - June 1999 LSAT, Section 3, Question 16 - page 337 in 10 More)
Evidence: People who had venereal disease in Beethoven's time often ingested mercury as a cure.
Conclusion: If there's mercury in Beethoven's hair, then he had venereal disease.

The argument is flawed because it confuses necessary and sufficient conditions (also known as the converse or mistaken reversal fallacy). Having VD is sufficient to lead to the conclusion that someone may have ingested mercury. (so if VD -> maybe mercury). However, this is not equivalent to saying that if someone ingested mercury, then they probably had VD. There may have been other reasons to ingest mercury. Perhaps it treated other diseases also.

If we negate each answer choice, we'll find the required assumption.

A. It doesn't matter if some mercury can be eliminated.
B. If everyone in Beethoven's time ingested mercury, then mercury in his hair is not proof of VD.
C. It doesn't matter if mercury is an effective treatment for venereal disease or not.
D. It doesn't matter if mercury poisoning causes deafness or not.
E. A comparison of Beethoven and Newton is not necessary.

B is correct.


5. Gutenberg Bible, B-36 Bible, Vinland Map, and presence of titanium (PrepTest 12 - October 1994 LSAT, Section 1, Question 24 - in 10 Actual)
This stimulus contains two arguments:

Argument 1
Evidence: Titanium is in both Gutenberg's Bible and the B-36 Bible

Conclusion: Gutenberg is the probable author of B-36 Bible.

Assumption: Gutenberg is the only person likely to have used titanium ink.

Argument 2
Evidence: Titanium is in both Gutenberg's Bible and the B-36 Bible (yes, same evidence as previous argument).

Conclusion: Vinland map could have been written in this time period.

Assumption: Gutenberg is NOT the only person likely to have used titanium ink.


Question stem: "The reasoning in the passage is vulnerable to criticism on the ground that..."

Explanation: This stimulus contains contradictory assumptions. It assumes that titanium ink is rare enough for Gutenberg to be the only person to use it, but it also assumes titanium ink was common enough for others to use it.

A is correct because it identifies this contradiction.

Answer Keys to LSAT PrepTests

Please see LSAT Answer Keys for Every PrepTest / Exam.

I've included answer keys for every single PrepTest in that blog post.

***

It's tempting to check the answer key at the end of each book of LSAT PrepTests after completing each LSAT question. I don't blame you for the impulse. However, checking your answers after each question slows you down during practice exams.

It also snaps you out of the test-day mindset and prevents you from predicting your performance. It's important to be able to guess how you did on a given section or exam. On test day, you'll want to make an informed decision over whether or not to cancel your LSAT score.

What should you do instead? Complete at least one section at a time, and preferably a full exam, predict how many you answered incorrectly per section, then mark your answers. If you just can't wait, complete at least a full section, then check your answers.

If having the answer key at the end of your book just proves too tempting, rip it out of each book and place all the answer keys in a folder in a safe place.

Unfortunately, lawyers tend to be fairly disorganized, and the same might be said of future lawyers. That's why lawyers have armies of paralegals, right? Unfortunately, you're not lawyers yet.

LSAT Logic in Alice in Wonderland

Lewis Carroll wrote Alice in Wonderland and Through the Looking Glass, but he was also a logician. This post will examine just a few aspects of formal logic he raised in his work.

Alice in Wonderland
On Wikipedia.
Free ebook.

"[Y]ou should say what you mean,' the March Hare went on.
'I do,' Alice hastily replied; 'at least — at least I mean what I say — that's the same thing, you know.'
'Not the same thing a bit!' said the Hatter. 'You might just as well say that "I see what I eat" is the same thing as "I eat what I see"!'
'You might just as well say,' added the March Hare, 'that "I like what I get" is the same thing as "I get what I like"!'
'You might just as well say,' added the Dormouse, who seemed to be talking in his sleep, 'that "I breathe when I sleep" is the same thing as "I sleep when I breathe"!'"

In the excerpt above, Alice makes the fallacy of mistaken reversal / converse (equating "X then Y" with "Y then X").

"at least I mean what I say" (from Carroll) = "whatever I say, I mean" (my translation)

Mapped out in the "if/then" structure, this becomes "If I say it, then I mean it" = say -> mean.

This is not equivalent to "say what you mean," (from Carroll) = "whatever I mean, I say" (my translation)

Mapped out in the "if/then" structure, it becomes "If I mean it, then I say it" = mean -> say.

In the excerpt above, the Hatter, March Hare, and Dormouse all point out the absurd results of this logical fallacy by switching the X and Y as Alice does.

"I say what I mean and I mean what I say" is overused in everyday life (perhaps as a result of "Alice in Wonderland"). For this reason, I'll demonstrate the mistaken reversal / converse with another example.

Example
The statement "I buy what I break" fits the classic china shop rule "If you break it, you buy it."

In "if/then" structure, this statement would read, "If I break it, then I will buy it." This means breaking it is a sufficient condition for buying it, but not the ONLY (or necessary) condition for buying it.

The mistaken reversal would be "If I buy it, then I broke it," which suggests breaking something is the ONLY condition under which you would buy something.

The bottom line: Despite Alice's seemingly normal behavior as our guide through Wonderland, the Tea Party's attendees have a better understanding of logic than Alice (in this example).

Word Ladder
Aside from writing children's books, Lewis Carroll invented a logic puzzle called the Word Ladder. In a Word Ladder, one word becomes another through several intermediate steps.

PrepTest 10, Section 2, Game 3 is a perfect example of a "Word Ladder."

In this game's setup, "'words' (real or nonsensical) consist of any combination of at least four letters of the English alphabet...[and] any 'sentence' consists of exactly five words." You create each new word when you delete, add, or replace one letter with another.

Although I can't publish the LSAT logic game's actual text here, a sentence in a word ladder might go something like:

clock -> click -> lick -> lice -> slice

In my made-up example, all 5 words happen to be real words, but word ladders don't always require this.

I'm fairly certain PrepTest 10 is the only one to contain a word ladder. However, this is no guarantee a word ladder won't come up again.

Law School Personal Statement Advice | Interview

I recently interviewed Linda Abraham, a law school admission consultant, via email. Our discussion follows.

1. What are some examples of successful "diversity statement" topics you've seen from applicants who are not traditionally classified as being racially diverse?

Diversity is not defined solely in ethnic terms in admissions. I have seen a background in the arts, sciences, or sports used as an effective diversity topic as well as unusual volunteer or international experiences. I have also seen disability used as a diversity topic. For non-URM’s the lessons and insights drawn from these experiences usually determine the effectiveness of these essays more than the actual experience.


2. Is it possible for an applicant to write a successful personal statement about a traveling experience or time abroad? If so, how?

Yes, definitely. In discussing a travel experience in a law school personal statement, the experience has to be meaningful and influential to the applicant. If it didn’t change the applicant in some way, forget it. The persuasive personal statement using a travel experience could start with a stellar moment on the trip, discuss how that scene is representative and seminal, and finally reveal its impact on the applicant. If the travel experience motivated the applicant to get involved and have impact or demonstrate leadership, all the better. Travelogues should be avoided at all costs.


3. Is it possible for an applicant to write a successful personal statement about why he or she wants to be a lawyer? If so, how?

Yes, but … the theme is neutral (and common). Execution counts. The admissions committee does want to “meet” the applicant through the personal statement, and if possible understand the applicant’s motivation and passion for law. So while not a required topic, it can work. If the applicant wants to use this theme, she must write in specific terms about the experiences that convinced her she wants to become a lawyer, the times she tested that interest, the particular aspects of legal practice she finds attractive, or the qualities and experiences that show she will be an excellent lawyer.


Linda Abraham, Accepted.com's founder and president, has helped many law school applicants gain acceptance to top law schools including Harvard, Yale, Columbia, Stanford, Boalt, and Chicago, and has written and lectured extensively on admissions. The Wall St. Journal, The New York Times, The Sunday Times of London, and BusinessWeek are among the publications that have sought Linda's expertise. You can find Linda at http://blog.accepted.com and http://www.twitter.com/Accepted

Photo by bobaubuchon

Scratch Paper on LSAT Logic Games?

UPDATE: For the Digital LSAT, you do get a booklet of scratch paper. It's about 12-14 pages, 8.5 x 11, unlined.

For the paper LSAT (outside North America), you can write on the page itself.


According to my highly unscientific survey, 95% of students draw their logic games diagrams / setups on separate sheets of paper while studying.

Actually, there was no survey - it's just something common I've noticed. Most students show up to their first tutoring session with me having done each logic game setup in a notebook. Each PrepTest page remains empty, even though there's no scratch paper on the LSAT.

Get used to using only the actual page instead of using a piece of scrap paper. It's essential that you get used to working within the test booklet's limited space.

Practice doing logic games in the LSAT test booklet, book, or photocopied page. If you must work on a separate sheet, only allow yourself 1/4 of a sheet per game. you can do this by folding the sheet in half twice. This will help you get used to making diagrams and symbols of the rules with minimal writing.

Berkeley / Boalt Hall Law School Admissions Dean | Interview

This is the 2nd post in the "Better Know a Law School" series. Edward G. Tom is the Assistant Dean for Admissions at the University of California, Berkeley, School of Law (Boalt Hall). In his spare time, Mr. Tom builds, plays, and collects guitars. Boalt Hall ranked 6th among law schools in US News and World Report this year.

1. Boalt Hall received media coverage in recent months for its "Law School Admission Project: Looking Beyond the LSAT." Would you please comment on your office's involvement, if any? If your office is not involved, what is its opinion regarding the LSAT in light of this project?

The admissions office has been involved to the extent that it provided demographic and statistical information to the research committee and the dean of admissions is a member of the committee. The Admissions Office concurs with the Committee that the LSAT remains a valid tool in determining admission decisions but should be only one of many factors taken into consideration. If there are other valid measurements of success in the profession - something the LSAT does not predict at all - then these tools should be considered for the future.


2. How has the student body changed in recent years?

The student body has evolved in step with society over the years. Perhaps the biggest change has been the level of interest in our interdisciplinary options. Many students are interested in taking advantage of how Berkeley Law can train them to be great lawyers who have a comprehensive understanding of policy issues.


3. In a typical year, what percentage of spots are still open on the day that applications are due?

About 25 percent.


4. In your opinion, what's the best rock band of all time?

That is too hard a question! Too many choices to narrow it to one! Candidates are Grateful Dead, Stevie Ray Vaughn, Steely Dan, Cream, and Led Zeppelin.

Correlation Between SAT and LSAT Scores?

Yes, there is some correlation between them. However, a low SAT score doesn't condemn you to a low LSAT score, and a high SAT score doesn't guarantee you a high LSAT score.

Some factors that limit the usefulness of any formula relating the two:

1. Brain cells killed while partying in college
2. Differences in your preparation for each exam
3. Differences in the nature of each test

However, I've received several requests recently for information about the relationship between SAT and LSAT scores.

This formula suggests with a moderate degree of certainty (note the qualifying statement here), what your LSAT score might be. I haven't seen any information regarding the origins of this formula, so if you have any, please let me know. This formula is not a prediction or guarantee: simply a suggestion.

LSAT = (SAT Math + SAT Verbal)/20.7 + 100.7

If you studied for 100 hours for the SAT, this formula provides a general guideline for how you might do on the LSAT if you study for 100 hours. Remember to take preparation into account. If you studied for the SAT and got a 1400, but your score prior to studying is only a 150, don't be discouraged. This just means that you have to study.

If you underperformed on the SAT but had a killer GPA in college, this means the LSAT is not likely to accurately predict your performance in law school. If this describes you, I recommend you write an addendum noting this.

For all the visual learners and statistics junkies out there, here's a graph displaying the correlation between SAT and LSAT (using a more complicated equation and a set of only 70 individuals). I found it here. It's far from comprehensive, but I'll share the info and let you decide.

LSAT Test Center Ratings and Reviews

Did you take the LSAT last week? Please add to these LSAT test center ratings and reviews!

If you haven't registered for the LSAT yet, take a look to help you decide where to register.

The comments on Columbia University's LSAT test center indicate that it's the sort of test center you'd want to avoid:

"Seemed there were too many LSAT test takers or we were moved because of the SAT II test takers, but were placed in an auditorium with pretty cramped seating. Proctors were quick/efficient. Desktop pulled up from arm rest, slightly smaller than the LSAT booklet."

3 Tips to Prepare the Day Before (and Day Of) the LSAT

If you've been studying for months and your timed practice scores are close to your desired LSAT score, just relax and take the day off. If you read my big list of LSAT Test Day Tips, you'll know everything you need to deal with Test Day.

However, if you haven't studied for very long, and if your practice LSAT scores are not close to your desired LSAT score, consider postponing your test date. There's no evidence that taking the LSAT before you're ready is any more effective or satisfying than setting your money on fire and stomping on it like a caveman.

Here are 3 quick tips to de-stress the day before (and day of) the LSAT:

1. Consider NOT using a timer.

Constantly being reminded of the passage of time can really stress you out. I like to think of a silent timer as a "Panic Attack in a Box."

People ask me, "How do I know when to go to the next question if I don't use a timer?" It's simple. When you think you should go on, go on. You're probably stressed about time without having a clock to remind you, so trust yourself to avoid getting stuck on any one question.


2. Focus on each LSAT question, not your overall LSAT score.

Thinking about your overall score and how each question affects it will only make you more nervous. This is the LSAT version of Lao Tzu's famous quote, "A journey of a thousand miles begins with a single step." Treat each question (step) separately as you proceed through the test (journey). Briefly pause between each question if necessary in order to clear your mind.


3. Get a fresh perspective on tough Logic Games.

If you begin to become nervous during the exam, particularly during Logic Games, stop for a moment and breathe deeply. Looking back at the game after a minute or two may give you a fresh perspective on it.

--
Good luck to everyone taking the LSAT tomorrow. Please let me know how it goes!

Virginia Law School Admissions Dean | Interview

This post begins "Better Know a Law School" -- a new series of interviews with law school admissions deans. First up is Jason Wu Trujillo, the Senior Assistant Dean for Admissions and Financial Aid at the University of Virginia School of Law. Virginia Law ranked 9th among law schools in US News and World Report this year.

1. What percentage of seats are reserved for in-state residents?

While the University of Virginia School of Law does not receive any state funding, we still reserve 40% of our seats for residents of the Commonwealth of Virginia.


2. What can wait-listed / deferred applicants do to improve their chances, and where is the line between an applicant's enthusiasm and obsession?

Wait-listed students can do many things to improve their chances of being made an offer. First, many wait-listed students will choose to retake the LSAT in February or even June. We have made offers from the waiting list due to the results of the June LSAT. If an applicant is still in school, the very best thing they can show is a strong final semester. They should update LSAC with their final grades as soon as they become available. Wait-listed applicants for whom Virginia is their absolute first choice should let us know. I will often receive a letter or email which states that, should an offer become available, the applicant will accept it unhesitatingly. That is a powerful statement and valuable information for me to have. If I have spots available, I will look to those applicants first.

There is a fine line between enthusiasm and obsession. A single letter of interest is sufficient. Even a letter or email once a month is fine. Beyond that, I think you run the risk of being too repetitive.


3. What makes Virginia Law unique? Would you please talk a bit about the student newspaper?

Virginia Law has a unique culture of collegiality. When I was choosing among law schools, I chose Virginia because the students seemed genuinely happy. Unfortunately there is no satisfaction quotient that one can use to measure this. I think the closest measure is the rate at which a school's alumni give back. In our most recent annual giving year, 52% of our alumni gave back to the Law School in the form of a financial contribution. That is #1 in the country and a statistic that truly demonstrates the satisfaction our alums have with their legal education. Moreover, more recent classes have been giving at rates in excess of 90%. If you can get 90% of newly minted lawyers to agree on anything, you are doing something right.

Our student newspaper, the Virginia Law Weekly, has won numerous awards for excellence. It has earned the American Bar Association's Best Law School Newspaper Award three years in a row.


4. Anything else?

I encourage interested students to visit Virginia. You are welcome anytime!

LSAT Reading Comprehension Tips and Tricks

or...How I Learned to Stop Worrying and Love the LSAT (Part 3 of 3)

Who do you think does better on the day of the LSAT - the person who enjoys reading or the person who hates it?

Part 1 of this series covered Logic Games, and Part 2 dealt with Logical Reasoning. This is Part 3.

I covered some passage-specific Reading Comprehension tips in 10 Strategies for LSAT Reading Comprehension. In this article, I share long-term reading comprehension strategies AND additional passage-specific techniques.

How to Improve Reading Comprehension and Concentration

Prevent "spacing out" by reading long analytical articles of the type found in NYTimes Magazine, the Atlantic, the Economist, Harper's, The Smithsonian, New Scientist, Scientific American, New Yorker, NY Review of Books, etc. You can generally subscribe to them via email and RSS.

The LSAT has no video section, so you'll have to increase your attention span by reading more. Daily newspapers aren't sufficient for this purpose. Instead of burying key information throughout the article as LSAT passages do, daily newspapers put important info at the beginning. They're catering to the public's short attention span.

Read about subjects that wouldn't normally interest you. You don't need to be an expert on the intricacies of nuclear fission, but it wouldn't hurt to skim a few science journals to see how scientists write. The same goes for philosophy and the humanities in general. The passage on Ronald Dworkin in PrepTest 35 is much easier if you already know something about legal positivism.


Comparison with Logical Reasoning

Much of what I've said about Logical Reasoning in previous posts applies to Reading Comprehension as well. Nearly every Logical Reasoning question has a parallel type in Reading Comprehension. Fortunately, the strategies for those questions apply to Reading Comp as well.

Of course, Reading Comp contains a few types of questions you won't see in Logical Reasoning such as "what is the author's attitude?" The "must be true" questions are often trickier as well.


Make a List of Reading Comprehension Vocabulary Words

More important than these minor differences is the vocabulary used in Reading Comprehension. The authors use language in a very precise manner, and you'll pick up on their nuances as you complete more passages. Maintain a list of RC words you don't use in everyday speech or see in everyday writing ("eschew" comes to mind). You may not know less common meanings of words like "qualify," and you might find you don't know the exact meanings of "ambiguity" and "ambivalence."


Read for the Passage's Structure, not its Content

I've said this in other posts, but it's worth repeating: the content of a LR stimulus or a RC passage is less important than its structure / argument. Always look identify the relevant portions of the argument (evidence or conclusion). "Speed-reading" techniques won't work because you're not reading for informational purposes.

You probably don't care about the regulatory, acclimatory, and developmental adaptive responses of overwintering macropterous/micropterous waterbugs (PrepTest 2). If you do, entomology's probably a more promising career path. If you insist on law, save your interest in the waterbugs for another time. The LSAT only requires you know these adaptive responses exist (after reading the passage) and where you can find them in the passage.

As you read, look for:

-the main points (conclusions)

-underlying facts (evidence)

-main players (supporters and critics)

-players' motivations / interests (if any)

Reading comprehension is a mechanical process, so treat it like a fact-finding mission. Search the passage for each of the things I've just listed.

Of course, it would be too easy if the answer to a main point (conclusion) question were worded exactly as written in the stimulus. For this reason, you need to be able to quickly find and identify each of these things so you have more time to recognize how they've been reworded in the answer choices. It helps if you're familiar with commonly-used terms in RC and their synonyms (covered in my previous RC post - linked above).


How to Read More Quickly

Don't pronounce words in your head as you read, and don't move your lips as you read. You can think faster than you speak, so if you cut off the connection between reading and speaking, you'll retain information even as you increase your speed.


How to Find the Main Point

First of all, it's the author's conclusion. Approach main point questions just as you would approach Logical Reasoning main point / conclusion questions. The main point is NOT the summary. It's simply what the author's trying to convince you is true. This will most closely resemble an opinion, rather than background info or undeniable facts. It can be at the beginning, middle, or end.

Depending upon the type of passage, the main point will take different forms.

If the passage is about a:

-problem, the main point is the solution.
-mystery (cause / effect), the main point should be the explanation the author advocates.
-person the author likes / dislikes, the main point is that the person is great / not great. Evidence will be reasons for opinion.
-study / experiment, the main point is that the study / experiment is good / bad. Evidence will strengthen / weaken study's validity by attacking study / people conducting it.

LSAT Logical Reasoning Tips and Tricks

or...How I Learned to Stop Worrying and Love the LSAT (Part 2 of 3)

Last week, I showed you how to answer Logic Games questions in my post on Logic Games tips and tricks. This week, I'll share the best ways to answer common Logical Reasoning questions. Next week, I'll show you how to prepare for Reading Comprehension.

First, why is it possible to conquer Logical Reasoning and even make it (sometimes) fun?

After doing a few sections of Logical Reasoning, you may feel like nuclear physics is an easier career than law. However, we hear flawed arguments all the time. I'm not talking about the ones you hear from your significant other, your parents, or your kids - I'm talking about advertising.

Imagine yourself reading the following argument on test day, and think about how you'd analyze it.

Stimulus:
"Advertisement: Purell hand sanitizer kills 99% of common disease-causing germs. Therefore, your health is in good hands when you use it."

A real LSAT question wouldn't use such a lame pun, but otherwise, I've based this on a real Logical Reasoning stimulus.

Purell may want you to believe their product will make you safe. My first question (and yours, too, I hope) is, "What about the other 1% of disease-causing germs (DCG)?" If any germs get us, it'll probably be those. This leads us to...

5 reasons this advertisement is flawed:

1. The 99% of common DCG Purell kills are the weakest 99%. The other 1% were too strong or difficult to kill. What I really need is a product to fight that 1%.

2. If enough other people buy and use Purell, then I don't need to worry about those 99% of common DCG. Purell's customers, and all the other purchasers of antibacterial products are taking care of the problem for me. I can sit back and relax (and be a "free rider"). Others will pay to eliminate the problem for me.

3. The advertisement fails to specify if it kills 99% of all common DCG or 99% of types of common DCG.

4. Is it worth bothering to get a product that kills common DCG? My body's probably encountered most common DCG - it has antibodies against them. If I've made it this far without the sanitizer, I don't need to worry about them. I need a product to fight uncommon DCG - they may be the greater threat.

5. I'm starting to sound like the paranoid scientist in a bad sci-fi flick, but hear me out on this last point. If everyone starts using a product that kills 99% of the common DCG, the 1% of common DCG will grow in number to replace the ones killed by the sanitizer. We'll have a growing army of DCG this sanitizer can't kill.

The previous argument should please health nuts concerned about worst-case scenarios, so here's one for smokers:

Stimulus:
"Joe developed cancer, and he smoked for many years. Therefore, smoking led to his cancer."

While this is possible, it's not certain. Correlation does not prove causation. The argument can be supported by 2 types of information:

1. Dismissers defend against possible alternative explanations.

Examples:

- Joe does not live in LA, a city known for its cancer-causing smog.
- Joe lives in the mountains, where there is little air pollution.
- Joe only eats organic produce, so he is exposed to very few pesticides.
- Joe does not work in a nuclear power plant.

2. Supporters strengthen the evidence or provide new evidence.

Examples:

- Studies show smokers have much higher cancer rates than the general public.
- Laboratory tests show cigarettes contain more carcinogens than anything else, ever.
- Smoking is the only cause of cancer.

(The LSAT is unlikely to include statements as extreme as some of the ones above, but see the sample question stem below. The question says "if true," so the answer choice can be unrealistic. Put aside your preconceptions.)

Any of the dismissers and supporters I listed above could be the correct answer choice to the following:

Question stem:
"Which one of the following, if true, would most strengthen the argument?"

You don't know if you're dealing with a dismisser or a supporter until you look at the answer choices.

Why? Because the correct answer doesn't need to be true for the argument to work. It just helps the argument if it is.

When it's a "Strengthen EXCEPT" question, 4 answer choices strengthen the argument, and 1 does not (it weakens OR has no effect). In these questions, it's worth trying to predict the strengtheners before looking at the answer choices - this helps you eliminate them more quickly.

If the question were "Which of the following assumptions does the argument depend upon?", it's a "necessary assumption" question, which is completely different.

Another example of an argument to illustrate how these question-types differ:

Stimulus:
"Child: Mommy, please let me play outside - I finished all my homework!"
(Argument: "Finish homework -> Play outside")

Question stem:
"Which one of the following, if true, would most strengthen the argument?"

Dismisser:
"The child has been well-behaved all day."

Supporter:
"Leading experts argue children need fresh air every day."

What if it were a principle question? These can function as strengthen questions, depending upon the stem.

Question stem:
"Which one of the following principles, if valid, would most help to justify the argument's conclusion?"

Principle:
"Children who perform their duties deserve to be rewarded."

Next week - why it's possible to improve on Reading Comprehension. If you just can't wait, see 10 Strategies for LSAT Reading Comprehension for another article I wrote about Reading Comp.