Yes and no, Amy. The contrapositive of any conditional statement is logically equivalent to the original claim. That is, they mean the same thing as each other, and are completely interchangeable. In that sense, taking the contrapositive isn't really an extra step, it's just recognizing that you can say the same thing two different ways.
Then again, it still requires
recognizing that what you are looking at is a contrapositive, so in that sense you do need to sometimes take that extra step, and when dealing with conditional statements you should always give consideration to the contrapositive.
One thing to keep in mind is that our method of using the "Unless Equation" is not the only way to handle the "unless" in the correct answer choice. There are those folks out there that choose instead to diagram "unless" as meaning the same as "if not", negating it and using it as a sufficient condition. Approached that way, answer C gets diagrammed from the start as:
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and there's no need to think about a contrapositive. We at PowerScore prefer our method, especially when the statement includes a multi-conditional "and" or "or" statement, but neither method is right or wrong, just different.
Short version: contrapositives are identical in meaning to the original conditional claims, so you can always use either one, and should always remain aware of that.
Keep up the good work!
Adam M. Tyson
PowerScore LSAT, GRE, ACT and SAT Instructor
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