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Logical Reasoning · Parallel Reasoning

PrepTest 134 · Section 2 · Question 3

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
Match a chain of if-then links that starts from a known fact and slides to a definite conclusion.
The basic logic
X-Ray the argument: a fact happened; that fact can happen only if a second thing happened; the second thing happens only when a third thing happened; so the third thing happened. Two forward links and one trigger. The right answer has the same chain, all valid, with the arrows pointing the same way.
Tiny words that decide it
  • “only”
  • “whenever”
  • “if”
  • “therefore”

Playground logic

Lulu's chain: the cookie jar is open (fact), the jar is opened only when Grandpa opens it, and Grandpa opens it only after dinner is finished. So dinner is finished (top bun). Two clean arrows, one trigger, a valid ending.

Step 2 · The kid story

Lulu and the Cookie Jar Chain

Tommy burst into the kitchen. 'The cookie jar lid is off! Somebody's sneaking cookies!' Lulu checked her clipboard. 'Rule one: the only person who ever opens that jar is Grandpa. Nobody else can twist the lid.' Tommy frowned. That was true; he had tried. 'Rule two: Grandpa opens the jar only after dinner is completely finished. He says so every night.' She looked at the open jar. 'The jar is open. So Grandpa opened it. And if Grandpa opened it, dinner is finished.' Tommy gasped. 'So dinner is over and I can have dessert?' 'Correct.' Marcus peeked in. 'I thought somebody stole cookies.' Priya sipped her juice box. 'Lulu followed the arrows forward, one link at a time. No guessing, no backwards steps.' Biscuit wagged, hoping the arrows led to him.

Step 3 · Try the model question

The only person who ever opens the cookie jar is Grandpa. If Grandpa opens the cookie jar, then dinner is finished. The cookie jar is open now. So dinner is finished.

Which argument follows the same pattern of reasoning as the one above?

Choices

Step 4 · The courtroom tale

The Case of the Ringing Bell Tower

Judge Ruth Okafor peered over her glasses. 'Mr. Whitfield, why do you say the festival has started?' Mr. Whitfield tugged his suspenders. 'Your Honor, the bell tower rang this morning. The only person with a key to that tower is the town keeper. And the town keeper rings the bell only when the mayor's festival flag goes up. The bell rang, so the keeper rang it. The keeper rang it, so the flag went up.' 'And the flag going up means the festival started?' 'By town law, yes.' The judge nodded. 'Every link points forward. I find the reasoning sound.'

Step 5 · Work the real question

Open PrepTest 134, Section 2, Question 3 in your official copy from LSAC (for example in LawHub) and read it there.

Your answer

How to apply it

X-Ray the stimulus first: write the trigger fact, each if-then link, and the conclusion as letters with arrows. Note that the conclusion is a definite fact and the chain is valid. Then X-Ray each choice the same way. Eliminate any choice whose conclusion is a general rule instead of a fact, whose arrows reverse, which uses an either-or, or which softens a link to 'usually'. Keep the one whose chain matches arrow for arrow.