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September 2017 LSAT
Gecko lizards are found in any environment where there is an abundant population of gnats. Gnats can survive only in ...
on August 26, 2019
Can someone please explain why A is incorrect? Thanks!
on August 27, 2019
The argument is a set of conditional statements:
(1) Gecko lizards are found anywhere where there is an abundant population of gnats.
AGP -> GL
(2) Gnats can only survive in wet climates.
~WC -> ~AGP
AGP -> WC
(3) Because there are no lizards, there must be not an abundant population of gnats.
~GL -> ~APG
This is a valid inference as it is a contrapositive of premise (1)
(4) The climate must not be wet.
~AGP -> ~WC
This is in an invalid inference, it is a mistaken reversal of premise (2). The only way this inference could be valid is if this statement was true:
WC -> AGP
If the climate is wet, then it has an abundant population of gnats.
Since the argument erroneously relies on this premise to form its conclusion, the correct answer choice is (B).
(A) is incorrect because the argument does not require that:
~AGP -> ~GL is true.
The argument makes a valid inference:
~GL -> ~AGP from
AGP -> GL.
Does that make sense?
Let me know if you have any further questions
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