An environmental engineer and land developer conducted a brown-field r

OFFICIAL EXPLANATION

Identify the Question Type:

The word “assumption” in the stem indicates that this is an Assumption question.

Untangle the Stimulus:

The word “therefore” signals the conclusion in the last sentence: the engineer’s methodology for the cost of reclaiming land was faulty. The evidence is that the cost for the REIT to reclaim the land was triple the engineer’s estimate.

Predict the Answer:

Faulty methodology is certainly a possible reason for the engineer’s bad estimate, but the author never demonstrates that it’s the only possible reason. The author must take for granted that nothing else besides a faulty methodology could have produced the engineer’s bad estimate.

Evaluate the Choices:

(E) matches the prediction and is correct. It rules out an alternate explanation for the bad estimate: that the engineer knew exactly what the cost would be and simply lied about it.

(A) is irrelevant. It doesn't matter whether the reclamation will be profitable; What matters is whether the engineer’s methodology was faulty or not.

(B) is an irrelevant comparison. Whether or not the engineer’s methodology was used multiples times has no bearing on whether that methodology is faulty.

(C) is also irrelevant, since any site other than the one in question is beside the point.

(D) merely confirms that the REIT's estimate is more accurate than the engineer's. This is irrelevant, since the argument is about why the engineer's report is inaccurate, and this doesn't explain that.

TAKEAWAY: Whenever an author argues that one thing must be the explanation for another, the assumption is always the same: that there are no other possible explanations.

The way I see it
This argument has a missing piece, it never blamed the land developer because he was also involved in arriving at the estimates.

Option E fills that gap. Says, that land developer was not involved in fudging the data, hence engineer alone to be blamed.

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Option (E) says that both Engineer and land developer were not involved in fudging the data.

A) Though more expensive than originally thought, the reclamation still would have resulted in a profitable development.
This does not affect the intended outcome therefore out

B) The environmental engineer did not study other reclamation sites and use the same methodology to estimate costs.
Whether the techniques were perfect or not dabatable and if there was some wrong formulaes in previous method then we cannot blame the engineers

C) The REIT had successfully reclaimed land in other developments during the past few years.
This is out context and doesn't have the slightest impact

D) A third party determined that the REIT’s methodology for determining the cost to reclaim the brown-field site was more accurate than that used by the environmental engineer.
Third party or not is not our concern

E) The engineer and land developer did not purposefully misrepresent the cost to reclaim the development site.
If they had purposefully misinterpreted then definitely the thing is not a mistake therefore for us this part has to be correct

Therefore IMO E

I received a PM asking me to comment on answer D. The "Official Explanation" doesn't discuss D correctly. They seem to dismiss D because it "doesn't explain" why the engineer's report might be inaccurate, but the question doesn't ask us to explain anything. It asks for an assumption, so it's asking for an unstated premise of the argument, something that is unsaid but that must be true for the argument to hold. And as long as we know (as the argument tells us) as a premise that the REIT discovered the cost was much higher than the engineer estimated, we don't need to assume anything about how the REIT determined that. Maybe the REIT assessed the cost themselves, or maybe they sought estimates from contractors, or maybe they brought in a third party -- it doesn't matter, because we know as a premise that they discovered the cost was much higher than anticipated. So D is not an assumption here, and is not the right answer.

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