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I'm writing explanations for LSAT 69, and I noticed something unusual. There are two necessary assumption questions where the correct answer is also a sufficient assumption. My impression is that this was rare on previous tests.

If I were explaining an older test, I'd google to see what other people said. But there isn't much discussion about the new LSAT yet. So you guys are my sanity check. Am I analyzing this right?

It's question 7, first LR section of the June 2013 LSAT. The one about the defective film. Here's my draft explanation. I think the assumption is both necessary and sufficient, let me know if I'm off base.

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QUESTION TYPE: Necessary Assumption

CONCLUSION: If the customer’s claim is correct, the store owes a refund.

REASONING: The customer says they handled the film properly. The film and camera worked.

ANALYSIS: Unusual. A necessary assumption question that uses linked conditional reasoning. Usually you shouldn’t diagram necessary assumption questions.

We have these facts:

1. Customer says handled correctly (C)
2. Camera not defective (CD)
3. Film not defective (FD)
4. not processed correctly --> refund (PC --> R)

If the store didn’t process the film correctly, it’s clear they owe the customer a refund. But none of the evidence leads to that. I’m going to draw the evidence on the left and the conclusion on the right:

C and CD and FD PC --> R

The author wrongly assumes they’re connected. To fix the argument, add an arrow connecting left and right. Here’s the missing premise:

C and CD and FD --> PC

If PC, then we can conclude ‘R’. Unusually, this answer is sufficient and necessary.

___________

A. We’re must prove the store owed a refund. This says what happens if they owed one. Not helpful.
B. CORRECT. This links the premises to the conclusion. This has to be true f0r the argument’s reasoning to work. Oddly, it’s also a sufficient assumption.
C. The pictures weren’t taken with a defective camera, so this tells us nothing.
D. The argument is talks about what happens if the customer’s claim is true, and they did handle the film correctly. This is irrelevant.
E. Same as D. This question is about what happens if the claim is correct.

I don't think this is that unusual, especially in more recent tests. I can't recall any particular question at the moment, but I know that I made note of a similar situation (paraphrasing, "N.A. essentially working as S.A. here") in my review of PTs a number of times.

Thanks. Come to think of it, the only recent explanations I've written are for LSATs 65-69.

I've done other tests with students, but I usually only notice this level of detail when I write explanations and think about each question for a while.

I remember noticing it a few times when writing for these tests, and not for older ones. So perhaps it's just a recent shift.