PrepTest 141 · Section 4 · Question 21 (Parallel Reasoning)

Step 1 · Pre-Question Guidance · read this first

Question type

Parallel Reasoning

The one idea it tests

Only two kinds exist; most of one kind has a trait; so if it is not the other kind, it probably has the trait.

The basic logic

X-Ray the skeleton: the only options ever have been A and B. Most B have trait T. So if the next one is not A, it will probably have T. The 'not A' condition is what forces B. Match the order of the pieces, the 'most', the 'probably', and the 'next one' scope.

Tiny words that decide it

“only”
“most”
“if not”
“probably”

Playground logic

Kevin's lunches have only ever been sandwiches or tacos (patty), and most tacos are messy (patty). Priya's top bun: if Kevin's next lunch isn't a sandwich, it will probably be messy. Ruling out one door leaves only the other, and the 'most' becomes a 'probably'.

Step 2 · The kid story

The Taco Forecast

Every day, Kevin brings a lunch, and every day it is either a sandwich or a taco. Never anything else. Marcus wanted to bet on tomorrow's lunch. "It'll be messy," he said. "Kevin's tacos are always messy." Priya shook her head. "Not always. Most tacos are messy. And we don't know it's a taco." She drew two doors on a napkin. "Kevin only ever has sandwiches or tacos. Most tacos are messy. So if tomorrow's lunch is not a sandwich, it's a taco, and then it will probably be messy." Lulu copied it onto her clipboard. "Close one door, walk through the other, and 'most' turns into 'probably.'" Kevin arrived with a taco. Salsa went everywhere, mostly on Marcus.

Step 3 · Try the model question

Every lunch Kevin has ever brought has been a sandwich or a taco. Most tacos are messy. So if Kevin's next lunch is not a sandwich, it will probably be messy.

Which argument has reasoning most like Priya's?

Step 4 · The courtroom tale

The Case of the Two Delivery Trucks

In a fictional city, a shop owner asked the court to guess her next delivery. Her lawyer stood. "Your Honor, the shop has only ever been served by the red truck and the blue truck. Most blue truck deliveries arrive late. So if the next delivery is not from the red truck, it will probably arrive late." Mr. Whitfield objected. "What if a green truck shows up?" "There has never been a green truck, counsel. Only red and blue." The judge nodded. "Two doors, one closed. The other has mostly late arrivals, so 'probably late' is fair." Mr. Whitfield muttered something about green trucks and sat down.

Step 5 · Work the real question

Open PrepTest 141, Section 4, Question 21 in your official copy from LSAC (for example in LawHub) and read it there.

Your answer

How to apply it

Write the skeleton: only A or B ever; most B have T; so if the next one is not A, probably T. Then check each choice against every piece. Is the 'only two' premise there? Does the 'most' belong to the right kind? Is the condition 'not the other kind'? Is it about the next one, not every future one? Does it keep 'probably', and point the arrow the same way? One broken piece kills a choice.