PrepTest 101

Incorrect. not Part-time job-some-Home for lunch. not Part-time job doesn't show up in the argument, and we can't make it by taking the contrapositive since Part-time job shows up only in a some statement, so this answer is out of scope.

Incorrect. Home for lunch → Part-time job. This answer let's us infer Walk to school → Part-time job, or the contrapositive not Part-time job → not Walk to school, but neither of those is the conclusion.

Incorrect. not Part-time job-some-not Home for lunch. This is a partial negation of the correct answer, failing to talk about students who do have part-time jobs.

Correct. Argument or Facts:
Argument

Valid or Flawed:
Flawed

Question Type:
Strengthen with Sufficient Premise

Stimulus Summary:
Walk to school → Home for lunch
Therefore - Part-time job-some-not Walk to school

Answer Anticipation:
It's much more common to see a quantifier/conditional inference show up in Must Be True questions; it's also a lot easier! Here, we'll have to figure out the missing piece that allows the conclusion to be drawn.

Let's start by getting the terms to line up. The shared term is Walk to school, but it's negated in the conclusion and not in the premise. Since we can't take contrapositives of some statements, we need to do so of the premise:
not Home for lunch → not Walk to school

With this done, we can see that we need to connect not Home for lunch with Part-time job. To get a some statement from a combination of a quantifier statement and a conditional, we need only a some statement, which are reversible, so we don't even need to figure out the direction here! Our answer will be:
not Home for lunch-some-Part-time job
Part-time job-some-not Home for lunch

(Note that there is a most statement that could lead to the same inference, but these Strengthen with Sufficient Premise questions generally have the answer that isn't stronger than required.)

Answer Explanation:
not Home for lunch-some-Part-time jobs This answer matches our anticipation. We know all students who don't go home for lunch also don't walk to school. If some of them also have part-time jobs, then some students who don't walk to school have part-time jobs, as the conclusion states.

Key Takeaway:
Knowing how to work with conditional statements and quantifier statements is key to picking up a few points on the LSAT. Be sure to drill these skills!

Incorrect. Home for lunch → Walk to school. This answer is the reversal of the premise so it doesn't add anything to the argument.