PrepTest 159 - Section 3 - Question 22 | Explanation & Discussion

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For a zoo to make a valuable contribution to the community, it must be well run. ███ █████ ████ ████ ███ ████ ███ ████ ████ █████████ █████████████ ██ ██████ ███ ████ █████ ████ ████ ███ ████ ███ ████ ████ █████████ ██████████████ ██ █████████ █████ ███ ████ █████ ████ ████ ████ ████████ █████████████ ██ █████ ███████████ ███ ███ ████ ███ █████ █████ ████ █████ ████ ███ ██████ ██ ███████

Use Formal Logic

If thinking about this question in English is easier for you than using formal logic, you need more practice gaining fluency in formal logic. Think of English and formal logic as two closely-related tools, like a hand screwdriver and a power screwdriver. While it’s true that any job you can complete with one you could also complete with the other, they each have niche uses in which they excel. If you find yourself tackling a line of 100 wood screws with a hand screwdriver, you need to get better with the power screwdriver.

Distilling The Premises

First, here’s an answer key of sorts – a clean, formal logic representation of all the claims:

(Domain: Zoos)
Claim 1: Valuable → Well Run
Claim 2: Large and Well Run → Full Time Vets
Claim 3: Small and Well Run ←some–> /Full Time Vets
Claim 4: Some Zoos: Large and Valuable and Open All Year
Claim 5: Small –most→ /Open All Year

Getting here involves a few advanced moves beyond simple translation:

We kicked the concept of “Zoos” into the domain, because in this argument there are no non-zoos.

We also combined a ton of similar terms. This is especially important – realizing when different English phrases both point to the same concept is crucial to reveal inferences. If you make a diagram where owns a young dog is YD and owns a puppy is P, you’re going to miss out on potential connections.

In Claims 2 and 3, we bundled “have some full-time veterinarians” into “Full Time Vets,” and treated “have only part-time veterinarians” as its opposite, /Full Time Vets.

In Claim 5, we treated “closed in winter” as “/Open All Year.”

Anticipating Inferences And Approaching The Answers

Note: Knowing your valid argument forms is key to this question’s anticipation regardless of whether you’re thinking in English or formal logic.

This section will thoroughly demonstrate how to play around with all the myriad ways these claims can be combined. You don’t need to read all of it now, and you certainly don’t need to do it all on test day. Realistically, you should spend a bit of time noodling around in this manner, then move on to the answer choices once you feel familiar with the general vibes.

For example, maybe you notice there aren’t any obvious ways to combine the “all” claims or “most” claims, and decide to roll into the answer choices with the idea of evaluating the “some” claims first. That would narrow your initial focus down to (C) and (D), potentially saving a ton of time.

But let’s start playing around with the inferences we can make, starting with the “all” claims, which are easiest to draw inferences from. First, it’d be nice to link Claim 1 up with Claim 2 or 3 via Well Run.

Claim 1: Valuable → Well Run
Claim 2: Large and Well Run → Full Time Vets
Claim 3: Small and Well Run ←some–> /Full Time Vets

We can’t do that, though, because both 2 and 3 have another sufficient condition (Large and Small, respectively). Our inability to make that link is notable. It gives us a preview of potential wrong answer choices, which could ask us to make that mistake.

Claim 1 is still nice, though: it lets us tack on Well Run whenever we see Valuable. (Don’t tack Valuable onto Well Run, though.) We can use that in Claim 4:

Claim 4+1: Some Zoos: Large and Valuable and Well Run and Open All Year

That’s a pretty cool deduction on its own, but even cooler is the door it opens up to Claim 2: these Zoos that are Large and Well Run and Open All Year also have some Full Time Vets (because of the Large and Well Run part).

Claim 4+1+2: Some Zoos: Large and Valuable and Well Run and Open All Year and Full Time Vets

Okay how about Claims 3 and 5, the ones about Small zoos?

Claim 3: Small and Well Run ←some–> /Full Time Vets
Claim 5: Small –most→ /Open All Year

Well, Claim 5 is a “most” claim linking Small to /Open All Year. Remembering our valid argument forms (link above), it could only link into an “all” claim starting with /Open All Year, or link up with another “most” claim starting with Small. Neither of those avenues are available to us.

Same general idea with Claim 3’s “some” claim, although fleshing all that out is a bridge too far. Complain in the comments if you want to zoom in here.

22.

If the statements above are █████ ████ █████ ███ ██ ███ █████████ ████ ████ ██ █████

Question Type

Must be true

Objective: Must Be True Questions

Must Be True questions present a series of claims in the stimulus, then ask us to provide an additional claim that can be validly inferred (i.e. on the spectrum of support, our answer choice must be super-duperly supported).

So it’s highly beneficial to spend time up front wrapping your head around the stimulus – simplifying or diagramming grammatically-complex claims, splitting out combined claims into two or more separate claims, etc. – and the dream is to generate your own inference(s) to proactively seek out in the answer choices.

That’s not always practical (sometimes it’s just hard, and sometimes there are too many to track), in which case using process of elimination – measuring each answer choice against the stimulus to ask “does this follow?” – is completely fine. But process of elimination or no, you need a crystal clear understanding of the stimulus.

As you evaluate the answer choices, remember that in general, weak claims are more likely to be true than strong claims – even without context, it is more likely that some glubsters are flubsters than it is that all glubsters are flubsters.

Most large zoos ███ ████ ████

Let’s try to link Large up with Well Run via a “most” claim (an “all claim would also be fine):

Large → ?? → ?? → Well Run

Well, Claim 1 gives us Valuable → Well Run. So we can get:

Large → ?? → Valuable → Well Run

If we had Large –most→ Valuable, we’d be cooking. Or if we had Large –most→ [Something] and [Something] → Valuable.

But we don’t.

No large, well-run ████ ████ ███ █████████ █████████████ ██ ██████

Translated into formal logic, (B) is a nearby version of Claim 2:

Claim 2: Large and Well Run → Full Time Vets
(B): Large and Well Run → /Part Time Vets

ooOo maybe Part Time Vets is the negation of Full Time Vets, eh? Like maybe if you’re not a Full Time Vet you’re a Part Time Vet and vice versa! That would do it.

But this connection is illusory. “Full Time Vets” as we defined it means “have some full-time vets on staff.” That concept is perfectly consistent with having some part-time vets too. (B) highlights a common difficulty that comes up when translating English phrases into Lawgic -- you often have to doublecheck your definitions to avoid equivocation.

Some zoos that ████ ████████ █████████████ ██ █████ ███████████ ████ ████ █████████ █████████████ ██ ██████

Translated into formal logic, (C) says:

(C): Valuable ←some→ /Full Time Vets

The nearby claims you might have used are 1 and 3:

Claim 1: Valuable → Well Run
Claim 3: Small and Well Run ←some–> /Full Time Vets

The closest-to-valid way to combine these looks like this:

/Full Time Vets ←some→ Well Run → Valuable

That structure would work, but it involves reversing Claim 1’s arrow.

28%

Some zoos that ███ ████ ███ ████ ████ █████████ █████████████ ██ ██████

It’s possible to anticipate this if you spend some time playing around, but the more realistic version of events is recognizing (D) as high priority because it’s a “some” claim and confirming it using the following logic or something like it:

(D) needs some zoos to be Open All Year and have Full Time Vets on staff.

Claim 4: Some zoos are Large and Valuable and Open All Year

Claim 1 says Valuable zoos are Well Run zoos, so those zoos from before are Large and Valuable and Well Run and Open All Year.

Claim 2 says zoos that are Large and Well Run have Full Time Vets on staff, so those zoos from before are Large and Valuable and Well Run and Open All Year and have Full Time Vets on staff.

So those zoos from before are, among many other things, Open All Year and have Full Time Vets on staff.

63%

Most small zoos ████ ████████ █████████████ ██ █████ ████████████

Let’s try to link up Small with Valuable using a “most” claim.

Small –most→ ?? → ?? → Valuable

For that, we need claims with Small on the left or Valuable on the right. Claim 5 feels like a promising starting place. It gives us:

Small –most→ /Open All Year → ?? → Valuable

Cool let’s find claims with /Open All Year on the left...

🪦RIP🪦

What about Claim 1? That has Valuable in it! But it’s on the left. We need a claim that lets us conclude something is Valuable, but Claim 1 is a claim that lets us conclude something else if we know that thing is Valuable.

What about Claim 3? That has Small on the left! Yeah but it’s a “some” claim. You can’t draw “most” claim inferences from “some” claims at all.

PrepTest 159 - Section 3 - Question 22

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