Lucinda will soon be attending National University as an engineering major.
Conclusion (therefore)
Lucinda will probably live in Western Hall.
Evidence
Lucinda will be attending National University as an engineering major.
At National University, most residents of Western Hall are engineering majors.
Evaluate
Given that ... most residents of Western Hall are engineering majors and that ... Lucinda is an engineering major How could we argue ... Lucinda probably won't live in Western Hall?
Do most engineering majors life in Western Hall? If not, then there's no reason to think that just because she's an engineering major that she'll probably live in Western Hall.
Suppose that Eastern Hall has 1000 students and Western Hall has 100 students. Most of the students in both dorms are engineering majors.
If all you know is that Lucinda is an engineering major, would you conclude that she's probably going to end up in Western Hall? No, it's a safer bet that she lands in Eastern Hall, since there are at least 501 engineering majors there whereas there are only at least 51 engineering majors in Western Hall.
To make the argument the author wants to make, he needs his Most premise to be reversed. If he had said this, it would be a valid argument:
Premise 1 - Lucinda is an engineering major Premise 2 - Most engineering majors live in Western Hall Conclusion - thus, Lucinda will probably live in Western Hall
The flaw is that his Most premise is backwards. Instead of telling us that Most people with the quality that Lucinda has (engineering major) live in Western, he told us that most people who live in Western have a quality that Lucinda has.
Goal
Since we see all these repeating symbols (Lucinda, western hall, national university, and engineering major are all mentioned twice), it makes sense to try to convert this argument into an algebraic recipe.
Premise1: Thing A will be X. Lucinda will be engineering major.
Premise 2: Most Y's are X. Most Western residents are engineering majors
Conclusion: Therefore, thing A will probably be Y. Lucinda will probably be a Western resident.
In terms of strategizing how we quickly see whether an answer is worth fully reading, let's look to see whether the first half of a Most claim is the backend of the conclusion. (i.e. in the original argument, "residents of Western Hall" was the first half of the Most premise and the second half of the conclusion)