#7 - Any fruit that is infected is also rotten. No fruit

[ay514]

Hello,

I'm looking at Question 7 on Section 2 of the June 2006 Practice Test.

From it, I get:

Infected --> Rotten
Inspected --> ~Infected
Inspected --> Safe to eat

So, from that, can I make the inference that ~Infected --> Safe to eat?

That is, if I have A--> B (or ~B) and A---> C B--> B (or ~B)? I hope this makes sense...I just wanted to know whether this way of reasoning was right or not. Thank you!

[Dave Killoran]

Without referencing the question, and just looking at your diagrams, the answer is no.

These are the two statements you provided that are relevant to the inference:

Inspected --> ~Infected
Inspected --> Safe to eat

or:

A --> B
A --> C
(I'll ignore the negatives above for the purposes of clarity).

The only inference that can be drawn from that relationship is B some C (or its reversible restatement, C some B).

Does that make sense? Please let me know. Thanks!

[ay514]

Thank you for your reply! Looking at just the diagram, I can see that it does not make sense, however, I guess my question applies more directly to the question. So I see that the assumption lies in linking "inspected" and "safe to eat" with "infected"... so for a question like this would it be better not to use conditional reasoning but instead just look for an answer linking the missing parts? I hope this makes sense! Thanks again for all your help!!

[Dave Killoran]

I always think of it as being contextual, meaning that I take my cues from what I'm seeing in the question. Sometimes using the arrows makes it easier, sometimes linking the missing pieces works better. This is part of the challenge of the LSAT: they alter each question so that different parts in each question have stronger or weaker roles. This puts you in the position of something similar to being an air traffic controller--you have to recognize what comes on your radar and then track it accordingly.

In this case, the first sentence doesn't play much of a role in the correct answer. Ignoring that sentence, we get:

Premise: Ins --> not Inf
Conclusion: Ins --> Safe

So, if we connect "not Inf" and Safe," we have the missing step, and that's what (E) does. Abstractly, what we see is:

Premise: A --> B
Conclusion: A --> C

(E): B --> C

In this case, I think you can do it either way, so it really depends on your personal preference.

Please let me know if that helps. Thanks!

[Dave Killoran]

Also, looking back at your original post, I see where things got confusing. This is a Justify question, but when you posted the original diagrams, you talked about inferring the statement. You can't infer it per se, but you can determine that that is the missing link that can be added to Justify the conclusion.

Thanks!

[jschruhl]

Hi,

I was wondering if anyone could help me figure out how to diagram/solve this question. I could not figure out how to link the different parts of the chain in any way that would lead me to the correct answer. Also, does the statement about Infected > Rotten do anything to this argument? It seems extraneous. Any help would be very much appreciated, been staring at this one for a while and it still doesn't make much sense to me.

Thanks!

[Nikki Siclunov]

This is a Justify question whose stimulus contains conditional reasoning. Here's the structure of the argument:

Premise: Infected Rotten

Premise: Inspected NOT infected

Conclusion: Inspected Safe to eat


The first premise is redundant, as neither of its conditions take part in the conclusion. We are looking for a Justify statement which, when combined with the second premise, gives us the conclusion. For instance, the conclusion would be justified if the following were true:

Justify Formula: NOT infected Safe to eat

With the help of that statement, we can build the following chain, whose additive inference proves the conclusion:

Inspected NOT infected Safe to eat

This prephrase reveals answer choice (E) to be correct.

[Sherry001]

Hello,
Can anyone please walk me through This question..? Here is my thought process . Hope I make sense to you .

1) infected it's also rotten
2)inspected -> not infected

C: inspected -> safe to eat

Question type : justify

A) nope it doesn't help me prove inspected , not infected .. Therefore safe
B) I'm having trouble eliminating this one. (not rotten -> safe ) doesn't this follow though ? Inspected - -> Not rotten & not infected -> safe to eat ?
If any fruit is infected is also rotten isn't a must be that if its not rotten it's not infected ?

C) we already know this inspected -> not infected

D) also had trouble eliminating this one . Infected -> not safe -> not inspected . Is this not contrapositive of inspected -> safe .

E) not infected -> safe connects p2 to the conclusion . It's correct .

Thank you very much
Sherry

[Jon Denning]

Hey Sherry,

Sure thing! First off, your process is spot on! Nice work! Still, since you asked for a walk through, let me break this question down and take it step by step.

This is a Justify question, so we need to provide new information in the correct answer choice that proves the conclusion is true. That in mind, let's begin with the conclusion.

The author concludes that any fruit that was inspected is safe to eat. The first thing to note about this is that "safe to eat" is totally new information, so it MUST be in the correct answer: you can't prove new info in a conclusion without tying that info back to some support premise(s)! Unfortunately all of the answers have "safe to eat," so that doesn't help us much here

Diagrammatically, the conclusion is:

Inspected Safe to eat

So what do we know about the other piece of the conclusion, "inspected"? Well we're told that no fruit that was inspected is infected, or:

Inspected Infected

This is actually a very common Justify scenario with conditional reasoning, and appears frequently in the easier Justify questions! You're told A B, and then the author concludes A C...how can you prove C comes from A, when all you know for sure is that B comes from A? Make C come from B: B C! That would connect C to A through the shared variable, B, and give you a chain: A B C .

In this case, if we could show that Infected indicated Safe to eat, we could make a chain:

Inspected Infected Safe to eat

And from that chain we could connect the first piece, Inspected, to the last piece, Safe to eat, and in doing so prove our conclusion:

Inspected Infected Safe to eat

Inspected Safe to eat

So which answer choice provides us with Infected Safe to eat? Answer choice (E), which means "if uninfected, then safe to eat":

Infected Safe to eat

A really great test of some fundamental conditional reasoning skills here, and a good indication of how you can prove conditional reasoning by creating chains that link pieces in a desired way.

Now, you may be wondering, "but what about the first sentence and the 'rotten' idea?" Turns out it's irrelevant here and plays no role in the argument. In other words it's there to distract you, but provides no help in proving the author's conclusion.

I hope that helps to reassure you, and clears up any uncertainties you might have had! Thanks again!

Jon

[Sherry001]

Awesome! Thank you . But just a quick question. ( clearly I need to visit my bibles again )!

I totally get this .
A->B
A->C
... A->B->C



But would this be correct as well ?

A->B
A->C
...A->C->B