Hi @MsLaurenLorde. These are drills designed to help you make deductions from premises. Here, you are given three premises, and asked to select the correct conclusion. The correct conclusion is a deduction that must be true according to the given premises.
The premises given are: P1: A ==> not B contrapositive: B ==> not A
P2: C ==> X contrapositive: not X ==> not C
P3: not C ==> B contrapositive: not B ==> C
Answer choice (B) must be true given these premises: not X ==> not A
How do we reach this conclusion? Take the transitive P1 + contrapositive of P3 + positive P2: A ==> not B ==> C ==> X. In other words: A ==> X. The contrapositive of this statement, not X ==> not A, is also a valid deduction.
Hope this helps! If you are having trouble with these foundational concepts, please take care to review our lectures on Sufficient & Necessary conditions and Intro to Logical Reasoning. This is truly the building block of the LSAT.
joryjesOctober 3, 2018
I don't understand why you couldn't have gotten the answer by doing: not x - > not c - > b - > not a Getting not x - > not a
Please explain
MehranOctober 16, 2018
@joryjes remember, the contrapositive is identical in meaning so these two are the exact same thing:
A ==> not B ==> C ==> X not X ==> not C ==> B ==> not A
So to answer your question, you could have gotten the answer by that method.
Hope that helps! Please let us know if you have any other questions.
