Q19 - Nearly all mail that is

[wayne_palmer10]

What would be the best way to attack this problem? Would you diagram it? I tried to, but the "nearly all" threw me off a bit.

[ManhattanPrepLSAT2]

I would not try to diagram this. I would try to understand the argument the best I could, then devote the majority of my time to the answer choices.

Because this is an inference question, I am not trying to completely understand the argument before looking at the answers. Instead, my focus is on matching an answer choice with the argument, and thinking about the reasoning that comes along with that answer choice.

(D) is the only answer that is consistent with the original argument. The others answer choices don't hold up when compared with the original argument.

See if this slight tweak in approach helps your timing and accuracy on inference questions.

[ManhattanPrepLSAT2]

Hi --

Nearly all and most are very similar, and if you are told "nearly all" it is generally sufficient to prove "most."

C is a very tempting answer, but it isn't actually what the argument says. Keep in mind that inference questions will have 1 right answer that is provable or almost provable, and 4 wrong answers that are definitely not provable -- so, the fact that something seems almost exactly like what the argument originally stated is NOT a reason to eliminate a choice.

The argument states "nearly all mail that is correctly addressed arrives at its destination within two days."

C switches this around to say most mail that arrives within two days is correctly addressed.

These are markedly different ideas. To illustrate: In life, we know nearly all sodas are less than $2, but that doesn't mean that most things that are less than $2 are soda. So, even if the first statement is true, we can't use it to prove the second.

Hope that helps!

[ManhattanPrepLSAT2]

Hi all --

It's clear this is a challenging question! Therefore, I thought it might be helpful if I posted an analogous argument with analogous answer choices.

We certainly appreciate your questions and the discussion they create, so please don't hesitate to let us know if the analogy doesn't clear things up, or if you have further questions.

Here are the corresponding elements in the analogy:

Mail correctly addressed = girls in a club
Mail incorrectly addressed = boys in a club
Arrives at destination in 2 days = loves steak
Arrives after 2 days = doesn't love steak
Damaged in transit = has vegetarian parents

"Nearly all girls in a certain club love steak. In fact, the only ones that don't have vegetarian parents. However, most people in the club don't love steak."

The question asks what MUST BE TRUE based on the information we are given.

Take a minute to think about what must be true. How can the minority of women, but the majority of people overall, not love steak? The only way is to have a greater difference among the men, but in the other direction (that is, a bigger difference in terms of the number of men who don't like steak being higher than the number of men who do like steak).

Let's examine some analogous answer choices:

(A) A large portion of girls must have parents who are vegetarians.

Does this have to be true? No. It could be that there is just one girl who's parents are vegetarians, or it could be more. We actually have very little information about this based on the facts we've been given.

(B) No boys love steak.

I think it's pretty easy to see why this is not provable based on the text.

(C) Most people who love steak are girls.

This is tempting, but this is not probable based on what we've been told.

Based on what we've been told, it could be true that...

Of 10 girls, 8 love steak and 2 don't, and, of the 10 guys (# of guys and girls doesn't have to be equal) 1 loves steak and 9 don't. Then we could say # of girls that like steak is greater than # of boys that like steak.

However, let's imagine we have 10 girls 1000 guys in the club. More guys than girls could love steak, even if the majority of guys don't love steak.

(D) Guys make up a large portion of the club

Does this have to be true?

Let's think about the facts we know:

Of the girls in the group, most love steak.
Of all the people in the group, most don't love steak.

Can the subset of girls who don't like steak in and of themselves make up the majority of all people who don't love steak? Absolutely not -- they are not even a majority in the subgroup of girls!

Knowing just about girls, we know that the category that loves steak has higher #'s (much higher, per the wording "nearly all") than the category that doesn't love steak. How do we make up for that and get to our overall tally? We need a significant portion of men that don't love steak.

This is essentially what we knew based on the facts, and this is the correct answer.

(E) doesn't have a great analogous equivalent, but I think it's an answer that is fairly easy to eliminate.

I hope that is helpful! And I hope it didn't make you too hungry!

[vredd418]

I chose (C), incorrect I know. But after looking at it, I used math to simplify it. Since "nearly all" = "most", you could say 99/100 "correctly addressed mail" arrives within 2 days. Then, since "most mail arrives 3 days or later", you could represent this as 101/200, or 501/1000. If you choose that first representation, then 101 arrive 3 days or later, 99 arrive within 2 days. If you choose the second representation, 99 arrive within 2 days, but 501 arrive 3 days or later. Both representations allow you to conclude a large proportion of mail is incorrectly addressed. But if you choose the second representation, you cannot say that "most" (greater than half) mail that arrives within 2 days is correctly addressed because of the total 499 that arrives within 2 days (1000-501), only 99 are "correctly addressed), which is not "most."

Perhaps this is a method someone could use on these proportion questions if you can do that math quickly. Of course you would have had to narrow down the choices to (C) and (D) (which I think would have been relatively easy to do here), then evaluated (C) with above method.

[zainrizvi]

Mail = 3 days
-------------------
Can be further divided into 2 categories correctly addressed and incorrectly addressed: CA can then be further categorized into damaged and not damaged.

IC = ???

------ AND

CA = 2 days
Damaged =? ND = 2 days


The key part is most CA is 2 days. No matter how much damaged mail you have, the MAJORITY of CA will always be 2 days. If overall is 3, then mail MUST be incorrectly addressed. That is (D).


...
Got this Q after like 4-5 months. Went through it 2-3 times but now I think I finally have a solid grasp lol

[noah]

I just sat down to take this LSAT and am glad to see some other people's heads were spinning from this one!

Thankfully I worked fast enough that I had time to come back and reason through it.

To the original question, I don't think you need to do all that math to solve this question, but it's great if you have that tool to bust out when needed.

I think this part of the last explanation is spot on

The key part is most CA is 2 days. No matter how much damaged mail you have, the MAJORITY of CA will always be 2 days. If overall is 3, then mail MUST be incorrectly addressed. That is (D).

I approached it similarly: if we need most mail to arrive in 3 days or more, how do we get that? We're not getting it from the correctly addressed mail, since nearly all of that is arriving within 2 days. So, that most must be coming from the other category, namely incorrectly addressed mail. This is what (D) gives us.

(A) is tricky but essentially unsupported. We know most correctly addressed mail arrives within 2 days. As for the part of that which is damaged, we have no clue - it might be a large part. Just because the correctly-addressed mail that takes longer is damaged doesn't mean that which is damaged will definitely take longer.

(B) is possible, but not assured. It might be that one incorrectly addressed letter arrives within two days!

(C) is tempting, since we need a lot of incorrectly-addressed mail to arrive late, however there could be A LOT of incorrectly-addressed mail, let's say 80% of all mail, and even if only 30% of it was squeaking in within two days, that would be 24% of all mail, more than the 20% of correctly-addressed mail.

(E) is unsupported - we don't know a thing about the relative amounts of mail that takes 3 days, 4 days, etc.

I hope that helps.

[mabelpaola]

okay so, only because this question had me very upset....

1. " nearly all mail that is correctly addressed arrives at its destination within two business days of being sent."

***so lets say of the 100 correctly addressed mail, nearly all arrive within 2 business days. = 99 out of 100***

2." in fact, correctly addressed mail takes longer than this only when it is damaged in transit"

***then there is only 1 out of 100 that is correctly addressed but arrives after 2 days because it was damaged in transit***

3. " overall, however most mail arrives three business days or more after being sent."

*** then the sent mail has to be at least more than 200, lets say 250. if it were less than 200 the correctly addressed and incorrectly addressed would be even (100 and 100). But since most mail arrives after 3 days this cannot be. So the correctly addressed is 100/250 and incorrectly addressed is 150/250.

150>100 and (D) is the correct answer. " A large portion of the mail is incorrectly addressed.

[Mab6q]

Here’s my two cents:
Let’s look at this from a basic conditional sense.
Nearly all mail that is correctly addressed will be used to mean All mail that is correctly addressed(as Mike Kim pointed out earlier)
Correctly addressed  Arrives 2 Days
Correctly addressed ~2Days  Damaged in transit.
Mail ---most --- > ~ arrive 2days
Pretty simple format to begin with.
A, Correctly addressed --- most --- > Damaged in transit . Incorrect. There is no way we can get to this from the conditionals. Don’t get confused by the first and second sentences. The second sentence says correctly addressed mail that DOES NOT ARRIVE IN 2 DAYS is damaged in transit. I think many people are interpreting it to mean that mail that does not arrive in 2 days is damaged in transit, and as such, they are attaching that to the last conditional to get A. No, that is not what the conditional say. So, we cant conclude from A that a large proportion of the mail that is correctly addressed is damaged in transit.
B, this is a mistaken reversal, and there is enough explanation above for why it is incorrect.
C, tempting but ultimately does not have to be true. This is simply a reversal of the first conditional (Correctly addressed  Arrive 2 Days ). I don’t think we should go past that because that’s LR 101.
D, yes, this follows. Mail ---most --- > ~Correctly Addressed. We know that Most mail does not arrive in 2 days, and if it does not arrive in 2 days, we get ~Correctly Addressed. As such, this can be inferred from the conditionals.
E, not even close. We cant infer this from the stimulus.

[michaelwcarper]

This is how I would explain the difference between
C. Most mail that arrives within two business days of being sent is correctly addressed
and
D. A large proportion of mail is incorrectly addressed.

As many people have commented, we have several kinds of mail. We have correctly addressed mail, which ALWAYS takes 2 days to deliver, UNLESS it is damaged, in which case, it may take 3 days. However, MOST of the correctly addressed mail arrives in 2 days.

Then we have mail in general, MOST of which takes 3 days. This group must be comprised of incorrectly addressed mail. However, there must be SOME incorrectly addressed mail which takes 2 days.

The reason that C is wrong is because that SOME of the incorrectly addressed, that does arrive in 2 days, may be larger in number than the correctly addressed mail that arrives in 2 days...if the total number of incorrectly addressed mail was relatively large.

Imagine if we had 100 total pieces of mail. 90 are incorrectly addressed, and of that 90, 80 (most) arrive in 3 days. This still leaves 10 incorrectly addressed pieces of mail that arrive in 2 days.

The other 10 are correctly addressed, and of that 10, 9 (most) arrive in 2 days. The remaining 1 was damaged and arrived in 3 days.

So of the mail delivered in 2 days, 10 are incorrectly addressed, and 9 are correctly addressed. Thus, "most mail that arrives within 2 business days" is NOT correctly addressed.

[sarahejlee]

Hey, I didn't see a problem with the word 'a large proportion' in the answer choice and got this right so I thought I'd give it a try. Against Mike's advice, I did diagram this (I'm a big fan of conditional diagramming and I can't help it. I would have tried otherwise if I saw this thread beforehand)

Premise #1: Mail & Correctly Addressed --nearly all or most--> within 2 business days.

Premise #2: (Mail & Correctly Addressed <--some--> /within 2 business days) --> Damaged in transit

N.B. The "Mail &" part of the above two diagrams can be omitted but I like to keep each and every detail they offer.

Premise #3: Mail --most--> 3 business days+
(where, 3 business days+ --> /within 2 business days)

From the contrapositive of the first conditional reasoning, we derive an inference that:

Mail --most --> 3 business days+ --> /within 2 business days --> /Correctly Addressed

Since 'a large proportion of mail' being incorrectly addressed is compatible with 'most' mails being incorrectly addressed, I went with (D).

HTH!

[pbookworm]

So, of course I wouldn't think about this while taking the exam, but this image helps.

The bigger circle represents all mail, whether delivered within 1 day, 2 day, 3 day, etc.

The medium sized circle represented all correctly addressed mail that is delivered within 2 days. I've sized it such that most mail still arrives three business days or more, as stated in the stimulus.

The smaller sized circle represents the correctly addressed mail that is damaged. Notice it is quite small with regards to the "CA" circle. This is because most correctly addressed mail arrives within 2 business days.

Hope this helps!

http://postimg.org/image/o2cj8edjp/

[jamiezheng]

hi i still have 2 questions on D and hope they are not too weird...

1. how do we know "incorrectly address mail" really exist? it's not mentioned anywhere in the question
2. say "incorrectly addressed mail" existed, how do we know it would take 3 or more days to arrives? (if it only takes, lets say, 2.5 days, D wouldnt stand)

since its a MBT question, if we dont know the answer with 100% confidence to my question 1 and 2, wouldnt choice A be equally correct (since A can be true but need not be true vs D incorrectly address mail can exist and can take more 3 or more days to arrive but need not be true since these information is not given)?


can someone help?

[jon.sesso]

Hi - Struggling here, even after reading this thread. Maybe this is just code for my need to stop studying.

Simply put - I think all answers are incorrect since the stimulus asks us what "must" be true. So my question is how can D be true?

To answer the inverse of that question, we'd have to identify a possible scenario for which the majority of letters sent are in fact correctly addressed.

Here's a scenario that I'd love for an LSAT geek to refute (I'm confident they will). First, what do we know?

Sentence 1: Almost all CA mail = 2- days (implying that a minority will take 3+ days)
Sentence 2: CA that is damaged in transit (DIT) = 3+ days
Sentence 3: Most mail (which includes CA, ICA, CA+DIT, ICA+DIT) = 3+ days. This implies that some mail takes 2- days.

Look at sentence 3 and notice we have exactly four variables: CA, ICA, CA+DIT, ICA+DIT. The question stem only takes into account the fact that, when all are added together, we can conclude that most mail takes 3+ days.

Here's what we don't know.
How long does ICA mail to arrive without DIT?

How long does ICA+DIT take to arrive?

D is telling us that this larger proportion that tips the scales to 3+ days MUST be due to ICA majority.

Now - if you're still with me (I'm intentionally going slow), here is the scenario for which D this question does not appear to refute:

What if we only have two variables instead of 4? In this case, we have CA (majority of which take 2- days) AND we have CA+DIT (3+ days). With this information in mind, now we can safely infer (based on what original data the question stem gives us) that a large proportion of mail (100% of it, in fact) is correctly addressed.

[ManhattanPrepLSAT1]

Hey jon.sesso, glad to see you feel the same way about this one as I do!

Over the years I've thought that there were a handful of questions (literally 5 or less) that I could disprove the credited answer choice. And over the years each one has fallen as my understanding of the stimulus, question stem, and answer choices became stronger. However, this is one that I think the LSAT may have gotten wrong and is the only remaining one that I think the LSAT got wrong. So, this one is simply the exception to the rule that of the other 8,000+ questions written by the LSAT, each one has an answer that can be proven by logic.

Here's my take on the stimulus...

CA -m-> 2Days
CA + ~2Days --> D
M -m-> ~2Days

Now the only way for answer choice (D) to meet the threshold of "must be true" is to reinterpret one of the statements. There's no way to infer M <-s-> ~CA from the statements I have above. But if you interpret "nearly all" as "all" you can make their answer work.

M -m-> ~2Days
~2Days --> ~CA

Therefore:

M <-s-> ~CA

But even this feels unsettling, since the inference would actually be M -m-> ~CA. But if you knew that most mail were incorrectly addressed, you could also say that a large proportion (some) mail is incorrectly addressed.

Not a great answer for you, I'm sure. But hopefully that helps!

[fmuirhea]

jon.sesso, if you assume that all mail is correctly addressed, then the first and third statements contradict one another because "most CA mail" and "most mail" would be equivalent. So, there must be mail that is incorrectly addressed.

[JinZ551]

Suppose we have 100 mails in total, including:
1. correctly addressed: 55
Not damaged 49 + damaged in transit 6
2. incorrectly addressed: 45

so we have 49 mails arrived within 2 days, and 45+6=51mails arrived more than 2 days.
does this match the scenario in the question stem?

how to define "a large propotion" in answer choise D?
does it mean "many" or "most" in logic?
can 45 be said to be "a large propotion"?

[Laura Damone]

Hi there!

"A large proportion" would be equivalent to "many." It doesn't necessarily reach the threshold for "most" because it doesn't imply over 50%. 45% would certainly constitute a large proportion.

To your numeric scenario:

If we had 100 pieces of mail, and we know that most mail doesn't arrive within 2 days, at least 51 pieces took 3 days or more.

Because nearly all correctly addressed mail arrives in 2 days or less, only a few of these 51 pieces could be correctly addressed. That means that a large proportion of them must be incorrectly addressed.

Hope this helps!

[hzj184]

Here is an example of why c is not a must true:

Correctly addressed mail = 100
Incorrectly addressed mail =10,000
Nearly all correctly addressed mail arrived within 2 days = 90
Most incorrectly addressed mail arrived after 2 days = 9,000
Some incorrectly addressed mail arrived within 2 days = 1,000

In this example, the C is not true.

[ChentuoZ870]

I take for a while analyzing why D is right.
It is hard to APRROVE that D is right directly, but we can easily DISAPPROVE its NEGATION.
consider the negation of D. the negation can be:

1.A large proportion of mail is correctly addressed.

another way to negate is:

2. not a large proportion of mail is incorrectly addressed.

here we take large as more than 50 percent. Since:

3. mail can only be EITHER correctly addressed OR incorrectly addressed.

then we can see 1 and 2 are equivalent. Let's see 1.
if 1 is true, then:
Nearly all mail that CA arrive within 2 days + A large proportion of mail is CA ----> a large proportion of mail arrives within 2 days.
and the conclusion above contradicts with the last sentences.

What is important is the EITHER/OR assumption here( if it is an assumption)

Or try to rephrase D in another way:
NOT a large proportion of mail is correctly addressed.
we could arrive to the conclusion above as follows:
premise1: most mail 3 days = most mail NOT within 2 days. (last sentence)
premise2: almost all mail CA within 2 days (first sentence)
conclusion: NOT most mail are mail CA = most mail are NOT mail CA.

for choice D, the damaged info is irrelevant, and most days with NOT CA is not required for D to be true.