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December 2013 LSAT
Auditor: XYZ, a construction company, purchased 20 new trucks 3 years ago, and there is no record of any of those tru...
on May 20, 2015
Could I please get an explanation for answer choice D?
on May 20, 2015
Here we have a strengthen with necessary premise question. Remember that a premise is necessary for a conclusion if the falsity of the premise guarantees or brings about the falsity of the conclusion. First we check to see if the answer choice strengthens the passage, and then, if it does strengthen, we negate the answer choice to see if its negation makes the argument fall apart. If the answer choice does both those things then it is our correct answer.
Conclusion: "none of the 20 trucks purchased 3 years ago were diesel powered."
Why? Because we know that XYZ purchased 20 new trucks 3 years ago and records do not indicate that any of those trucks were sold last year. Records also indicate that XYZ sold off all of its diesel-powered trucks last year.
Well, the first thing that should irk you is that these 20 trucks were purchased 3 years ago and based off the fact that there are no records that they were sold last year, we assume that none of them are diesel-powered, since XYZ sold off all its diesel-powered trucks last year.
So, let's look at answer choice (D): "None of the 20 trucks was sold before last year."
Did this strengthen the argument? Yes. This addresses the hole in the argument that the trucks could have been all purchased 2 years ago, leaving the possibility for them to--in fact--be diesel-powered trucks. Because if they were all purchased 2 years ago, the remaining diesel-powered trucks that were sold 1 year ago were not amongst that group.
Negation of (D): at least one of the trucks was sold before last year.
So, if at least one truck was sold before last year, then it could have been a diesel-powered truck. Therefore, the conclusion--that NONE of the 20 trucks purchased 3 years ago were diesel powered--no longer stands if we take the negation of answer choice (D) to be true.
Hope that clears things up! Please let us know if you have any other questions.
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