Diagram This... Forum

[suspicious android]

Sure, if it got administered it would end up being the first time in history that an entire logic game was removed from scoring after the fact.

Why do you say that? Just because there can be ambiguity in the wording of such a game doesn't mean there would have to be.

[TheKingintheNorth]

If it is not the case that the park contains both laurels and oaks, then it contains firs and spruces.

Diagram:
(not)L or (not)O ===> F & S
(or neither)

there are no tricks here

~L => F AND S
~O => F AND S (I used commas: F, S; instead of writing out and or using dots and such)

the contrapositive would be
~F, ~S => L or O

The contrapositve is a cumbersome tool. It can be helpful, but it takes up a bit of precious time and can be (like it is here) unwieldy and not really worth it. So when you have clear rules like my two initial ones, best to keep in the back of you mind.


that's the best "diagram" for that rule to use to combine it with other rules when you make inferences (which are the bread and butter of these grouping games). Another rule might lead to ~O for example, then boom, easy inference without even thinking about it.

[Jeffort]

The LSAT writers have never used the word apart in any LG rule and probably never will due to context related ambiguity of meaning.

They used "apart" once in a specific question (where the question adds a rule) but not in a way where either interpretation made any difference. (PT 19 Sec 1 Q 6)

If the inspection of G and of H are scheduled, not necessarily in that order, for days as far apart as possible, which one of the following is a complete and accurate list of the factories any one of which could be scheduled for inspection for day 1?

I stand corrected. I meant in a rule in the game stimulus/set of conditions though. That example is likely one of a few if not the only unambiguous way they can use it in LGs to keep things clear.

[Jeffort]

Sure, if it got administered it would end up being the first time in history that an entire logic game was removed from scoring after the fact.

Why do you say that? Just because there can be ambiguity in the wording of such a game doesn't mean there would have to be.

I suppose they could get all wordy and also include another rule that defines what 'apart' means in the context of the game. Otherwise, as Earlcat described, when put into the context of LSAT games, especially linear/sequencing games, things get a bit blurry.

Apart could mean the two elements don't occupy the same slot in the sequence (one isn't sitting on the others lap) or it could mean spaces in the sequence in between the two elements. For it to be clear in order to pass LSAT quality control and test specs in terms of the meaning of the conditions themselves being unambiguous from the text they would have to include extra text to explicitly define numerous things.

[Ocean64]

can somebody find an official LSAC example of an assumption that is both necessary and sufficient?

I'm curious to see what that looks like.

[Ocean64]

can somebody find an official LSAC example of an assumption that is both necessary and sufficient?

I'm curious to see what that looks like.

I guess no one was able to find an example of this. Super Prep says that an assumption can be both sufficient and necessary at the same time.

anyways, i have another question...

lets say If A then B (A===>B)

question: can this be stated as "either B or not A"?

if anyone can give me any variation on how "either/or" can be used to state an "if/then" relationship I'd very much appreciate it.

[KevinP]

can somebody find an official LSAC example of an assumption that is both necessary and sufficient?

I'm curious to see what that looks like.

I can't remember any off of the top of my head. Not entirely assumption-related, but if the statement can be expressed as "if, and only if", then it is both a sufficient and necessary condition.

I guess no one was able to find an example of this. Super Prep says that an assumption can be both sufficient and necessary at the same time.

anyways, i have another question...

lets say If A then B (A===>B)

question: can this be stated as "either B or not A"?

Yes.
A --> B and ~A OR B are logically equivalent, which by definition means their truth tables are the same.
Logical Equivalence : (p → q) = (¬p ∨ q)
https://secure.wikimedia.org/wikipedia/ ... plications
https://secure.wikimedia.org/wikipedia/ ... rder_logic

if anyone can give me any variation on how "either/or" can be used to state an "if/then" relationship I'd very much appreciate it.

A OR B is the same as ~A --> B

[EarlCat]

lets say If A then B (A===>B)

question: can this be stated as "either B or not A"?

Yes. You'd probably be most likely to see this in games.

if anyone can give me any variation on how "either/or" can be used to state an "if/then" relationship I'd very much appreciate it.

~A --> B
Either B or A (implied or both).

Edit: whoops, didn't see KevinP's reply. My bad.

[Ocean64]

thank you, now we're getting somewhere. btw this was in relation to PT 28, Sec 1 (LR), Q 20.

this variation is nowhere to be found in the LRB, LGB or any LSAT material I've seen. it should be though.

[EarlCat]

thank you, now we're getting somewhere. btw this was in relation to PT 28, Sec 1 (LR), Q 20.

this variation is nowhere to be found in the LRB, LGB or any LSAT material I've seen. it should be though.

Noted. One day I will write an LSAT book and this will be in there.

[Ocean64]

Please evaluate the validity, explain and if possible diagram the following argument:

Most people in Glendale buy gasoline on Mondays only. But almost everyone in Glendale buys groceries on Tuesdays only. It follows that fewer than half of the people in Glendale buy gasoline on the same day on which they buy groceries.

[suspicious android]

Most people in Glendale buy gasoline on Mondays only. But almost everyone in Glendale buys groceries on Tuesdays only. It follows that fewer than half of the people in Glendale buy gasoline on the same day on which they buy groceries.

Not worth diagramming, but not valid. Imagine exactly 100 people in Glendale. The people who don't buy gas on Mondays (up to 49) could buy their gas on Tuesdays, giving us perhaps 49 residents who buy gas and groceries on the same day. The people who don't buy groceries on Tuesday, even if that's just just one person, could buy their groceries on Monday, giving us another one or more persons buying gas and groceries on the same day. So we could have 50 or more people buying gas and groceries on the same day.

[Ocean64]

Not worth diagramming, but not valid. Imagine exactly 100 people in Glendale. The people who don't buy gas on Mondays (up to 49) could buy their gas on Tuesdays, giving us perhaps 49 residents who buy gas and groceries on the same day. The people who don't buy groceries on Tuesday, even if that's just just one person, could buy their groceries on Monday, giving us another one or more persons buying gas and groceries on the same day. So we could have 50 or more people buying gas and groceries on the same day.

i thought about this for quite a bit. this problem is not as simple as it appears to be. consider this:

1. pretend that Glendale has only 3 people who live in it, JKN. this will simplify majority/minority and visualization best.
2. the key is not who buys gas/groceries on what day and who doesn't, it's who is allowed to REPEAT the purchase during the week and who isn't. key word in the stimulus is "only".
3. after much contemplation, it became apparent to me that had the commodities of gas & groceries been available only on Monday and Tuesday respectively, the argument's conclusion would have been sound.
4. There are more days in the week than just Monday and Tuesday when such commodities are presumably still available.

let me know what you think.

[suspicious android]

Not worth diagramming, but not valid. Imagine exactly 100 people in Glendale. The people who don't buy gas on Mondays (up to 49) could buy their gas on Tuesdays, giving us perhaps 49 residents who buy gas and groceries on the same day. The people who don't buy groceries on Tuesday, even if that's just just one person, could buy their groceries on Monday, giving us another one or more persons buying gas and groceries on the same day. So we could have 50 or more people buying gas and groceries on the same day.

i thought about this for quite a bit. this problem is not as simple as it appears to be. consider this:

3. after much contemplation, it became apparent to me that had the commodities of gas & groceries been available only on Monday and Tuesday respectively, the argument's conclusion would have been sound.

Not sure what you're getting at. As it is, the argument is invalid. If we restrict ourselves to Monday and Tuesday, it is still invalid, that's the whole point of my example. If there's a problem with my hypothetical, you could try to attack that, but... well, there isn't. It is a tricky argument, but not valid. There are other valid hypotheticals that can disprove it, but all you need is one to disprove the conclusion.

[Ocean64]

nevermind my previous post, i know the argument is invalids, i'm trying to see why

i need your help applying your explanation to make it more tangible.

Glendale has 100 people.
lets pretend that:

Monday: 51 people got gas (and this is the only time they can do it), and 49 did not as you said, then..

Tuesday: 49 people (those same people who did not buy gas on Monday...correct me if wrong) buy both gas and groceries on Tuesday, plus 2 people who buy only groceries on Tuesday (to meet the "almost everyone" rule), which adds up to the simple majority of 51 people who only buy their groceries on Tuesday . and now we have 49 people who did not buy grocery on Tuesday, so now we take one or more of those 49 people and have them buy their groceries on Monday? who else is buying groceries on Monday exactly and from which group?

i don't understand, did i make a mistake somewhere?

[suspicious android]

Most people in Glendale buy gasoline on Mondays only. But almost everyone in Glendale buys groceries on Tuesdays only. It follows that fewer than half of the people in Glendale buy gasoline on the same day on which they buy groceries.


Let's say 51 people buy their gas on Monday, from Exxon which is right next to the grocery store Ralph's.
Let's say 99 people buy their groceries on Tuesday, from Lucky's, right next to the gas station BP.

So that one guy who doesn't go to Lucky's on Tuesday, might be a guy who goes to Exxon and Ralph's on Monday. That gives us 1 guy (Joe) who buys his gas and groceries on the same day.

Those 49 people who don't go to Exxon/Ralph's on Monday might be a large family that goes to Lucky's/BP on Tuesday. That gives us 49 people (the Wilsons) who buy their gas and groceries on the same day.

Joe + the Wilsons makes exactly half the town that buys gas and groceries on the same day. So the conclusion that fewer than half do that? Not necessarily true.

[Ocean64]

Most people in Glendale buy gasoline on Mondays only. But almost everyone in Glendale buys groceries on Tuesdays only. It follows that fewer than half of the people in Glendale buy gasoline on the same day on which they buy groceries.


Let's say 51 people buy their gas on Monday, from Exxon which is right next to the grocery store Ralph's.
Let's say 99 people buy their groceries on Tuesday, from Lucky's, right next to the gas station BP.

So that one guy who doesn't go to Lucky's on Tuesday, might be a guy who goes to Exxon and Ralph's on Monday. That gives us 1 guy (Joe) who buys his gas and groceries on the same day.

Those 49 people who don't go to Exxon/Ralph's on Monday might be a large family that goes to Lucky's/BP on Tuesday. That gives us 49 people (the Wilsons) who buy their gas and groceries on the same day.

Joe + the Wilsons makes exactly half the town that buys gas and groceries on the same day. So the conclusion that fewer than half do that? Not necessarily true.

I see...my thought process was too narrow, i thought the argument was saying that less than half of the people must buy both gas and groceries on the same day of the week, as opposed to whenever during the week, which for Joe was to buy both Monday and for the wilson's to buy both Tuesday. thanks suspicious android!

[Ocean64]

"The fact that Brooks has a part-time job does not by itself explain why he is doing poorly in school. Many students with part-time jobs are able to do well in school."


this is supposed to be a valid argument, but I keep thinking that just because some other students are doing well with part-time jobs, that doesn't mean this will apply in Brooks' case, he may be a struggling student who needs every hour of study, and the job alone is hindering his school.

can anyone please explain?

[Jeffort]

"The fact that Brooks has a part-time job does not by itself explain why he is doing poorly in school. Many students with part-time jobs are able to do well in school."


this is supposed to be a valid argument, but I keep thinking that just because some other students are doing well with part-time jobs, that doesn't mean this will apply in Brooks' case, he may be a struggling student who needs every hour of study, and the job alone is hindering his school.

can anyone please explain?

Source/reference for the question please. Is this a real LSAT question and what source presents it is a valid argument?

The argument you present is about causation.

Since a premise dictates that many other students in the same situation (have a part-time job) are able to do well in school, the argument effectively rules out working part-time as being the SOLE cause behind why Brooks is performing poorly, thereby proving that there must be some other contributing cause(s) while also making it clear that it is NOT concluding that his job had no causal role behind his poor grades.

.

[Ocean64]

this is from TestMasters prep material, 2009 edition; Lesson 6 Page 18 number 18, they ask to identify whether the argument is valid.

i was thinking about the "by itself" portion. while having a part time job may not have been sufficient reason for other students in Brooks' position to do badly, it may have been sufficient in his particular case to derail his schooling. i feel like the one premise doesn't do a good job of supporting the argument. thoughts?

[suspicious android]

this is from TestMasters prep material, 2009 edition; Lesson 6 Page 18 number 18, they ask to identify whether the argument is valid.

i was thinking about the "by itself" portion. while having a part time job may not have been sufficient reason for other students in Brooks' position to do badly, it may have been sufficient in his particular case to derail his schooling. i feel like the one premise doesn't do a good job of supporting the argument. thoughts?

Like Jeffort said, the part-time job isn't enough to explain his poor performance, because part-time jobs aren't always associated with poor school performance. Sure, it might have been too much for Brooks, because Brooks is probably a dumb ass. His dumb-assness in conjunction with the part-time job may have caused poor performance, but that's why the part-time job does not by itself explain the performance.

[Ocean64]

got it.
since if part-time job was causation, it would have produced the same result in all the cases, but since it did not, then "by itself" is not the sole factor of Brooks doing bad. thanks!