Logical Reasoning

PT140 · S3 · Q19 Auditor: XYZ, a construction company

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Auditor: XYZ, a construction company, purchased 20 new trucks 3 years ago, and there is no record of any of those trucks being sold last year.

Conclusion (thus conclude)

None of the 20 trucks purchased 3 years ago were diesel powered.

Evidence

None of the 20 trucks purchased 3 years ago were sold last year.

All of the company's diesel trucks were sold last year.

Evaluate

Because this argument seems to have more to do with numbers and a timeline (rather than conditional logic rules and term shifts), we'd probably anticipate a Defender type answer, rather than a Linking one. In order to figure out what sort of Objection the correct answer may defend against, let's try to make an Objection.

Given that ... all the company's diesel trucks were sold last year and that ... none of the 20 that were bought 3 years ago were sold last year, How could we still argue that ... some of the 20 that were bought 3 years ago were diesel?

At first we feel trapped by the logic, because if they were diesel, then they would have been sold last year, but we were told that none of these 20 were sold last year. What does this timeline look like?

3yrs ago 2yrs 1yr (last year) Now bought sold all diesel these 20 trucks sold none of the 20

The wiggle room lies in the 2yrs ago gap. It's possible that some of the 20 trucks we bought were diesel, and that those got sold 2 years ago (or any time in between when we bought them and last year).

2018: bought 20 trucks (only 1 was diesel) 2019: sold that 1 diesel 2020: sold all other diesels we owned 2021: still have those other 19 trucks from 2018

Goal

The one way to beat this argument is for the company to have bought a diesel truck 3 years ago but sold it prior to last year. That avoids the intended conflict between "last year we sold all our diesels" and .

Since this is Necessary Assumption, we would look for an answer that rules out that objection: .

If we never "solved this riddle", we would just go to the answers thinking,

19.

Which one of the following is an assumption required by the auditor's reasoning?

All of the trucks that
Too Strong: all
We know that 100% of the company's diesels were sold last year. The author doesn't need to assume that 100% of what the company sold last year were diesel powered. If we negate this and say, "the company also sold some non-diesel trucks last year", that wouldn't weaken. It wouldn't allow us to argue that some of the trucks from 3 years ago were actually diesel.
21% picked this
XYZ did not purchase any
Out of Scope: used trucks
The conclusion is only about the 20 new trucks that were purchased 3 years ago. The argument wouldn't care if the company also purchased used trucks, since the conclusion will still be purely about the new trucks.
4% picked this
XYZ did not purchase any
Out of Scope: other new trucks
The conclusion is only about the 20 new trucks that were purchased 3 years ago. The argument wouldn't care if the company did or didn't also purchase new trucks since then, because the conclusion will still be purely about the 20 new trucks from 3 years ago.
13% picked this
Correct
None of the 20 trucks
Why this is right
If we negate this, it's saying that "some of the 20 trucks were sold prior to last year". That opens up the door to the Objection scenario we were considering. It's possible that 3 years ago, they bought these 20 trucks, some of which were diesel, and then they sold those diesel trucks 2 years ago. The only reason the author is convinced that none of the 20 were diesel is because the company sold off all its diesel last year but none of the 20 were sold last year. Note: just because we say "none of those 20 trucks were sold last year" doesn't mean "the company still possessed all 20 of those trucks". The author is assuming it does. His argument works if we know that all 20 of those trucks are still possessed. That would guarantee that none of them are diesel, since all the diesel trucks this company possessed were sold last year. This is a weird example of a correct answer on Necessary Assumption that is basically a Sufficient Assumption. And when we negate this, it weakens by creating some doubt -- the negation makes it possible that one of these 20 was diesel and that it was sold before last year. The negation doesn't actually refute the original argument, but a negation does not need to "destroy the argument", as students often say, in order to be the correct answer. We can think, "Which answer, if negated, most weakens", and the winner of that will always be the correct answer on Necessary Assumption.
Skill tested: Necessary Assumption · how this choice captures the argument's function is the move to repeat next time.
57% picked this
XYZ no longer owns any
Out of Scope
Out of Scope: more than 3 years ago This argument only cares about the trucks that were purchased 3 years ago, so there aren't any assumptions needed about trucks purchased more than 3 years ago.
5% picked this

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