QUESTION TYPE: Parallel Reasoning
CONCLUSION: Even settling –> poured while ground was dry OR crack
REASONING: Wet –>
Solid Foundation –> Settle Evenly or Crack
ANALYSIS: I solved this question in 20 seconds. I just looked at the structure of the conclusion, which said “either A or B will be true”. Only one answer, A, matched that structure.
That’s the easy way, and probably how you should solve a question like this under timed conditions. But, if you’re really interested in the structure of arguments, you can follow along with the rest of this explanation to see how this is a good argument, and why the conclusion is true.
Get a pencil and paper and draw it yourself, this is easily the least intuitive argument I’ve found in logical reasoning, ever. What follows is only for advanced students.
Let’s review the logic. The stimulus gives two conditional statements. They join on “not having a settled foundation.” I’m drawing the diagram with acronyms, look at the reasoning section above if you’re not sure what they refer to:
SF –> SE or C
C –> SF –> W
I’ve drawn the contrapositive as well.
Now, the question does something with logic that I’ve never seen any other LSAT question do. The conclusion is a correct deduction, but if you read the diagram left to right, you won’t see it. Let’s take a look at why the deduction is nonetheless true.
Look at the contrapositive diagram. There are two sufficient conditions: settling evenly, and not cracking. We need both to prove the necessary.
If the concrete settles evenly, there are two possibilities: either the concrete cracks, or it doesn’t:
C –> SF –> W
If the concrete doesn’t crack, then we can conclude SF and
W. (Not wet is the same as dry. There’s no in between with wet and dry.)
If the concrete does crack….well, that was the conclusion, right? Either the foundation is dry or it will crack. Voila.
So the two possibilities in the conclusion just describe the concrete either cracking or not cracking.
- CORRECT. This conclusion matches the “either/or” structure from the stimulus. That’s really all you need to know, since every other answer fails this test.
That said, here is the diagram that shows this really matches the structure of the stimulus:
Band D–> PE –> WP
Not Blurred is the same as poured evenly in the stimulus, and the two exclusive possibilities are either dark or not dark, which proves the conclusion “dark or working properly”. See the analysis above for the full explanation.
- This says “both properly exposed and properly developed”. We’re looking for something that says either/or.
- This says “the camera is working properly”. We’re looking for something that says either/or.
- This says “the photograph will not be dark.” We’re looking for something that says either/or.
- This says “A or B –> Will not work properly”. We’re looking for something that says “A –> either B or C
Author’s note: Here’s how I really approach parallel answers: I look to see if the conclusion matches the structure of the conclusion in the stimulus. The harder the argument, the more likely LSAC left you a shortcut by allowing you to quickly eliminate wrong answers for structural reasons. If I still have two answers after looking at structure, then I focus more narrowly, but often only one answer is left.
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