LSAT 38, Logical Reasoning I, Q22, LSATHacks

LR Question 22 Explanation, by LSATHacks

QUESTION TEXT: Damming the Merv River would provide irrigation…

QUESTION TYPE: Parallel Reasoning

CONCLUSION: Building a dam wouldn’t help agricultural productivity in the region.

REASONING: A dam would help the upstream lands but hurt the downstream lands even more.

ANALYSIS: This is a good argument. It shows that benefits in one area are outweighed by benefits in another area. The overall effect (on agriculture) is negative. The conclusion is mild: it only says the overall effect is not positive. 

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1. This compares across areas (health vs. taste) whereas the stimulus compared agricultural benefits to agricultural drawbacks. Also, this doesn’t tell us that the benefits of less disease definitely outweigh the worse taste.
2. This argument might be correct, but we would have to know whether businesses would also reduce their transatlantic phone calls.
3. CORRECT. This compares time saved to time lost, and finds that time lost in city delays offsets time saved by the new highway. The conclusion matches the stimulus: it merely says the highway will not reduce transit time (actually, the highway would increase transit time.) 
4. This is a bad argument. If an illness can’t be cured by rest alone then you ought to see a doctor. It only says diseases can often be cured at home.
5. This is a bad argument. It could be that the only plants damaged by the chemical are weeds. In that case, many gardens could benefit.