Q7 - Any fruit that is infected

[leweeg]

Picked D.

I was looking for ~I->E to complete the assumption.
(I = Infected; INS = Inspected and R= Rotten; E=safe to eat)

Given,

I->R
INS->~I
---------
INS -> E

I assumed (D) ~E->I whose contra is ~I->E

Answer is (E) E->~I. can someone help me out?

[giladedelman]

Your analysis of the stimulus is right on, but you seem to be misinterpreting the answers choices.

Notice that "rotten" is a total red herring here. What we care about is making the connection between "inspected --> not infected" to "inspected --> safe to eat." So like you said, we are pretty plainly looking for an assumption that says "not infected --> safe to eat."

That's exactly what (E) tells us. It is safe to eat any food that is uninfected, so IF it's uninfected, it's safe to eat it. "Not infected --> safe to eat."

(A) and (B) both deal with rottenness, which will not help us get to "inspected --> safe."

(C) is out because we know that all inspected food is NOT infected -- so we don't care about food that IS infected.

(D) tells us that if a food is infected, it's not safe to eat it. "Infected --> not safe." This is the negated version of what we want; incorrect.

Does that answer your question?

[kmewmewblue]

Infected→Rotten (This is red herring)

Inspected→/Infected

-------------------------

Inspected→Safe to eat

Missing assumption:
Inspected →/Infected→Safe to eat
(E) says this.
"That" implies sufficient so "uninfected" will be sufficient and "safe to eat" will be necessary.

A→/B
-----
A→C

Missing assumption:A→/B→C

[ManhattanPrepLSAT1]

Nice work kmewmewblue in identifying that the first premise is a red herring! Not easy to do, and not all that common on Sufficient Assumption questions - though something that should never be out of consideration.

[cdjmarmon]

How can we identify rotten as a Red herring?

[timmydoeslsat]

We can see that rotten will not be able to play a role in reaching the conclusion from the evidence.

INF ---> R
INF ---> ~INS
___________
INS ---> S


I take a page out of Matt Sherman's book by lining up my sufficient conditions in an identical manner when possible. It makes the gap easy to see.

When we have a sufficient assumption question stem like we do here, we want to see what our conclusion is. In this case, it is a conditional statement. Thus, we want our evidence to start off with the initial claim in the conclusion.

So we need to ask ourselves how can INS reach S from the evidence. We will start by considering what INS gives us from evidence. We know that we would have ~INF.

And we do not have S into evidence. So we could link up ~INF to S. This would give us a valid conclusion.

Notice that the R claim will not get us to S. For us to arrive at S, we need to know if INS. When we have INS, we have ~INF, and when we have ~INF, we have nothing in evidence.

We do have if INF, but that will get us nowhere in reaching our conclusion.

[mkd000]

I get the argument and all, but how does "not infected" = "uninfected". For example, if something is not known, this is not the same as something being unknown. Please help! Am I looking too much into this? Or is this a legit weird LSAT situation.

[tommywallach]

Hey Mkd,

I don't quite understand the question. If you are uninfected, you are not infected. If something is unknown, it is not known. Those are the exact same thing!

-t

[abdelmalak17]

I was just curious whether my diagramming is correct. As followed are my abbreviations:
INF= Infected
R=Rotten
INS=Inspected
S= Safe to eat
~= Not
Any fruit that is infected is also rotten. : INF-->R (in my opinion, this first sentence is irrelevant)
(Premise 1) No fruit that was inspected is infected. : INS-->~INF A-->B
(Conclusion) Any fruit that was inspected is safe to eat. : INS-->S A-->C

Missing Premise is obviously B-->C
So, the correct answer: E. It is safe to eat any fruit that is uninfected. : ~INF-->S
Let me know if I did everything correct on this sufficient question. Thanks in advance.

[ohthatpatrick]

You did everything correctly.

The first conditional MIGHT have mattered if it chained with the second conditional, but since they don't chain together and since the conclusion wants a connection between inspected and safe, you're correct that the 1st sentence ends up being irrelevant.

Nice work!

[abdelmalak17]

Thank you, "ohthatpatrick"! You have been helping me so much with your responses throughout the forums!

[tiwinkle12]

Are there any other types of questions like this where there are sneaky irrelevant statements or clauses?

[Yu440]

Hello,

I got the this question wrong (I was wavering between B and E) and now I understand why upon review and diagramming. So my question is, should one diagram these sorts of questions during the actual test? Or do most people figure the logical relationships out in their heads? Thanks!

[ohthatpatrick]

I think this is a good example where high scorers WOULD diagram this, to make sure they're getting directionality right.

Conditional logic is easy to mess up if you don't have a precise mental picture of what's on the left / what's on the right. These are the types of questions that most people get wrong, because our intuitive reading abilities aren't well-groomed for interpreting conditional logic correctly all the time.

Diagramming definitely takes a little extra time, but we only have to do it on like 5 of 50 LR questions, so it's fine to go there when needed.

When would you potentially diagram?
- Sufficient Assumption (if there's tricky conditional logic)
- Principles
- Inference (if there's tricky conditional logic)
- Matching (if there's conditional logic)