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Logical Reasoning · Parallel Reasoning

PrepTest 151 · Section 2 · Question 19

Phase 1 (your first ~400 questions): read the guidance, then answer. No clock.

Step 1 · Pre-Question Guidance · read this first

Question type
Parallel Reasoning
The one idea it tests
If something happened, and it could only happen when two things were both true, then each of those things is true.
The basic logic
X-Ray the stimulus: Result happened. Result requires A and B. So A. That is a valid move. Match an answer with the same bones: an outcome that occurred, a 'needs both' rule, and a conclusion naming one of the two needed things.
Tiny words that decide it
  • “impossible without”
  • “both”
  • “so”

Playground logic

Tommy got a gold star (it happened). Gold stars need both homework done and a tidy desk (the rule). So Tommy did his homework (one piece of the 'both'). Bones: happened, needs both, so one is true.

Step 2 · The kid story

Tommy's Gold Star

Tommy bursts through the door waving a shiny gold star. "Look!" Lulu taps her clipboard. "Ms. Rivera has a rule. Nobody gets a gold star unless they turned in homework AND kept a tidy desk. Both." Marcus squints. "So what?" "So," says Lulu, "Tommy got the star. That means he turned in his homework." Tommy looks proud. Then he looks worried. "Wait, does that mean my desk is tidy too?" "Yep," says Lulu. "The rule says both. But I only needed one to prove my point." Grandpa chuckles. "That's clean thinking, kiddo. Something happened, it needed two things, so each one must be there." Priya adds, "Just do not flip it. A tidy desk alone does not earn a star."

Step 3 · Try the model question

Tommy earned a gold star today. Ms. Rivera never gives a gold star unless a student both turns in homework and keeps a tidy desk. So Tommy must have turned in his homework.

Which argument follows the same pattern of reasoning as Lulu's?

Choices

Step 4 · The courtroom tale

The Case of the Launched Rowboat

The rowboat left the dock at dawn. The harbor master testifies: "No boat leaves my dock unless it has a signed permit and a life jacket for every rider. Both, every time." Mr. Whitfield rises. "Your Honor, my client says she never got a permit." The judge peers over her glasses. "Counselor, the boat left. Your own witness says it cannot leave without both. So a permit was signed." Mr. Whitfield tugs his suspenders. "Well, at least we know the riders were safe." The judge nods. "That follows too. But it does not help your client."

Step 5 · Work the real question

Open PrepTest 151, Section 2, Question 19 in your official copy from LSAC (for example in LawHub) and read it there.

Your answer

How to apply it

X-Ray the stimulus into bones: what happened, the rule that it needs two things together, and the claim that one of those two is true. Then X-Ray each answer the same way. Throw out any that reverse the rule, that work with only one needed thing, that use 'or', or that end with a weaker or different kind of claim. The keeper has all three bones in the same order of logic, even if the sentences are shuffled.