Q20 - Normal full term babies are born with

[griffin.811]

I see why the other answers are incorrect, but why is D correct aside from being "more right" than the others?

The Stimulus pretty much says B is not a member or group A because it exhibits something C that no member of group A has.

D says B is not a member of group A because it does not exhibit something C that all members of group A exhibit.

Isn't the structure reversed here?

Thanks

[patrice.antoine]

Hey Griffin!

Any reason why there is another variable (C) for this stimulus? When I approached this question I diagrammed using only two variables: (A) and (B) and the contrapositive of same.

The stim states that If A (normal full-term babies) then B (born with X that disappears by age 2 of two months).

But we have this baby that's 3 months that still exhibits these reflexes. I simply diagrammed this as (Not B) - this baby is not a baby whose reflexes disappeared by age 2 - therefore, (Not A).

Premise: A --> B
________________
Conclusion: Not B --> Not A


(D) pretty much follows the same logic chain:

If you're an opossum (A) ---> have abdominal pouches (B)

but this opossum doesn't have abdominal pouches (Not B), therefore, not an opossum (Not A).

[griffin.811]

Hey Patrice, thanks for picking this one up!

I used 3 letters because I felt there were 3 variables: A - full term babies, B the reflexes that babies have, and C this other type of baby.

I don't usually diagram, it's just not something that comes natural to me (except in LG's). I more or less just strip the subject matter and look for an answer that reaches the same type of conclusion, via premises used in the same fashion as the stim.

Your response though, showed me how B could be ~B which cleared this one up for me.

Thanks!

[ohthatpatrick]

Griffin, you're not alone in your reluctance to diagram.

Just a couple things to keep in mind going forward:

1. Diagramming comes naturally to ALMOST NO ONE

2. MOST questions don't have any need for diagramming

So ... where does that leave us? It leaves us with the idea that maybe only 10-15% of LR questions actually lend themselves to diagramming.

Since 85-90% of LR questions don't need diagramming, we often think to ourselves, "Hey, I'm generally doing fine without diagramming. Why add that unwieldy process to my thinking?"

Here's the problem: you and most other people will continue to get those 10-15% of questions wrong (or at least struggle to get them right) on every test.

In many cases, these formulaic, almost mathematically logical questions are what separates the wheat from the chaff (or the 170s from the 160s).

You want to have this sort of filter:
1. Initially read it like you normally would for ideas/understanding.
2. Are you struggling to put it together? Are you noticing conditional trigger words? Are you feeling a very mechanical / logical structure to the ideas (i.e. does it feel like "Idea Math" rather than a persuasive conversation?)

When #2 starts happening, you switch to a more logical / diagrammed way of looking at the stimulus.

Common sense and keen reading are NORMALLY all you need, but continue to develop your ability to think about an argument in its abstract form so that you have the necessary tools to deal with those types of questions.

What are THOSE types of questions? Mainly:
Match the Reasoning (like this one)
Sufficient Assumption
Inference (only the ones that feature conditional wording)
Principle Justify + Apply the Principle (you'll probably be okay with most of these, but sometimes the direction of the logic is difference between the right and wrong answer)

Good luck.

[uhdang]

You want to have this sort of filter:
1. Initially read it like you normally would for ideas/understanding.
2. Are you struggling to put it together? Are you noticing conditional trigger words? Are you feeling a very mechanical / logical structure to the ideas (i.e. does it feel like "Idea Math" rather than a persuasive conversation?)

I used to wonder when I should apply diagramming and worried if I am using too much of it, so this filtering process tip is awesome. Thanks, Patrick.

And, since I was feeling "very mechanical and logical" for this question , I solved it with mechanical approach.

Looking at the stimulus,

Normal => no reflex (disappear in two months)
reflex (still exist after two months) => Not normal

We can conclude that this is a contrapositive form. Now, all we need to do is to find another contrapositive form from answer choices.

A)
CO2 => turns limewater milky
Oxygen (~CO2) => ~turns limewater milky
>> Mistaken Negation.

B)
Ape => ~talk
Suzy => Ape
Suzy => ~talk
>> Logically sound but not contrapositive.

C)
Human => Social animals
Henry => Social
Henry => Normal
>> Logically not sound. Where did "normal" come from?

D)
Opossums => abdominal pouches
~abdominal pouches => ~Opossums
>> Match. This is it.

E)
“some” trees => shed leaves annually
~shed leaves => ~normal.
>> Not sound. Just like C), where did "normal" come from?

The correct answer is D)