Q15 - Zach's Coffeehouse schedules free

[john]

15. (D)
Question type: Inference

If Zack’s offers half-price coffee all day on days that there are poetry readings, and there are poetry readings on almost every Wednesday, then Zack’s offers half-price coffee all day on almost every Wednesday: that’s what choice (D) says.

(A) gets its reasoning backwards: just because most Wednesdays have poetry readings, we can’t conclude that most poetry readings happen on Wednesday, and therefore that most coffee deals happen on Wednesday.
(B) makes the same error as (A), in a more straightforward manner.
(C) also engages in reverse logic: all poetry reading days feature a coffee deal, but we can’t conclude that all, or even most, coffee deal days feature poetry readings.
(E) is incorrect because, while we can conclude that there are some Wednesdays without poetry readings, it doesn’t follow (for reasons similar to those given with choice (C)) that those Wednesdays definitely don’t have coffee deals.


#officialexplanation

[kmewmewblue]

I still don't understand the explanation.
Is this Formal Logic?

HPC　→ FPR →(most)Wed.
inference: HPC →(most) Wed.

But then, what does "if not all Wednesdays." mean in (D)?

Help please!

[legalrabbithole]

Please correct me if I'm wrong, but this is how I diagrammed the problem.

The stem is worded awfully, but I basically zoned in on "every" since that indicates a sufficient condition.
Wed -most-> free poetry reading --> 1/2 priced coffee

Correct answer:
To answer the above poster's question, I saw "most if not all wed" as saying "most wed" since most is 51-100 (includes all).

So (D) diagrammed, looks like this: W -most-> 1/2 priced coffee

[alana.canfield]

Hello,

I was hoping someone could give me a logic-based meaning for the phrases "almost every" and "most, if not all" that are in the stimulus and correct answer (D), respectively, of this question.

To me it looked like no answers to this question were correct because I interpreted the stimulus phrase "almost every" to mean "most, but not all". And then I interpreted D's "most, if not all" to mean "most" in the traditional sense, which allows for all.

Should I be interpreting "almost every" to mean "every"? What effect does "almost" have in logic?

Thank you,
Alana

[chike_eze]

Please correct me if I'm wrong, but this is how I diagrammed the problem.

The stem is worded awfully, but I basically zoned in on "every" since that indicates a sufficient condition.
Wed -most-> free poetry reading --> 1/2 priced coffee

Correct answer:
To answer the above poster's question, I saw "most if not all wed" as saying "most wed" since most is 51-100 (includes all).

So (D) diagrammed, looks like this: W -most-> 1/2 priced coffee

I like this explanation. And I too had a similar logical construct.

Wednesday -- most --> Poetry --> Half Coffee all day
> Inference: Wednesday --most--> Half Coffee all day

Honestly, "most if not all" threw me off which led me to hastily choose (E) on my first go around. But on further inspection I decided "most if not all" means "most or all but not both". Which is equivalent to 51% - 100% -> which is equivalent to "most".

> I would appreciate comments from experts on the "most if not all" construct. Is this logically equivalent to "most" ?

[maryadkins]

> I would appreciate comments from experts on the "most if not all" construct. Is this logically equivalent to "most" ?

Yes! Good. And I agree--good explanation legalrabbithole.

I interpreted the stimulus phrase "almost every" to mean "most, but not all".

I would think of it this way too. But (D) still works. Because "if not all" (and you've defined this now as if not all), then most.

(D)'s "most if not all" just means most, yes. Because it doesn't actually tell you that you can have all. It tells that if you don't have all, you have most.

Hope this clarifies.

[ddebarr20]

I read 'most if not all' as 'all' or 'most'. I agree that 'most' could mean 'all', but it doesn't necessarily. 'All' does necessarily mean 'all'. 'Most' could be equivalent to 'almost every', 'all' could not. I think the question makers wanted you to look at the 'all' in choice D) vs the 'almost every' in the question stem, and become confused. This does seem like a change of degree error, but if you look further, you see that just because poetry is sufficient to have half-priced coffee, it isn't necessary. Zack's can serve half-priced coffee anytime it wants, not only on poetry reading days. Therefore, it could serve on the almost every Wednesday when there is poetry AND the few Wednesdays when there is not poetry.

To put it simply, I don't think 'most if not all' was meant to be so scrutinized, it was more the 'all' vs 'almost every' that was intended to trick people...and it was intended to be tricky because of the potential for confusion regarding the sufficiency vs necessity of poetry to half-priced coffee.

[nflamel69]

Can any geeks clarify this?

I noticed no one mentioned the term shift from free poetry readings to poetry readings between the 2 sentences. When I was taking this test timed, I didn't see it either. But after I caught it during review, my diagram is something like this:

W most FPC (free poetry reading)

PC (poetry reading) -> HPC (half priced coffee)

So is it safe to say that FPC -> PC? I feel this is the only way that we can infer this. and I think it works logically too, as free poetry reading is a subtype of poetry reading, so it is enough to trigger poetry reading.

Any thoughts? I honestly think if LSAC decides to make this question hard they would definitely play something into this.

[amil91]

Can any geeks clarify this?

I noticed no one mentioned the term shift from free poetry readings to poetry readings between the 2 sentences. When I was taking this test timed, I didn't see it either. But after I caught it during review, my diagram is something like this:

W most FPC (free poetry reading)

PC (poetry reading) -> HPC (half priced coffee)

So is it safe to say that FPC -> PC? I feel this is the only way that we can infer this. and I think it works logically too, as free poetry reading is a subtype of poetry reading, so it is enough to trigger poetry reading.

Any thoughts? I honestly think if LSAC decides to make this question hard they would definitely play something into this.

The distinction between 'free poetry readings' and 'poetry readings' does not matter to answer this question. Think about it like this, Zack has half price coffee whenever he has a poetry reading. On most Wednesdays he has free poetry readings. A free poetry reading is still a poetry reading.

[cyt5015]

Logic Chain:
Wed(most)-->free poetry reading-->poetry reading-->half priced coffee all day

(A). You only can infer that on most Wednesday, Zack offers half priced coffee, but you don't know whether Zack offers coffee on other days or not.
(B) You can infer that on most Wednesday, Zack offers free poetry reading, not the reverse.
(C) This is almost a reverse to the statement "Zack offers half priced coffee on every free poetry reading day".
(E) You can't negate the "some" or "most" conditional chains.
For example: most A is B. Can we infer some A is not B? No, that is not necessarily true. Hope that helps.

[ohthatpatrick]

Nice, compact write-up.

As a quick recap of some of the recurring questions/confusion:

- almost every = most but not all (51-99%)
- most if not all = most (51-100%)
- free poetry readings = a type of poetry reading

If anyone still has lingering qualms, let us know.

[civnetn]

I just want to clarify something that I think has been tripping most people on this thread up. I'm not sure if it's been entirely clearly explained.

(D) States, "Zack offers half-priced coffee all day on most if not all Wednesdays."

"Most if not all," does not mean, "Most BUT not all." It means "Most but possible all days."

This answer choice is correct for the same reason E is incorrect.

We are told that Zack serves half-priced coffee on every day that a Poetry Reading is scheduled. And we know that Zack schedules poetry readings on ALMOST every Wednesday. But what we don't know is if on days that he doesn't schedule poetry readings (which could be Wednesday) he doesn't serve coffee. It's entirely possible that Zack wouldn't schedule a poetry reading on Wednesday, but still serve free coffee.

Therefore, it's true that Zack offers half-priced coffee all day on most and possibly all Wednesdays.