Logical Reasoning · Sufficient Assumption

PrepTest 124 · Section 2 · Question 22

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

Step 1 · Pre-Question Guidance · read this first

Question type

Sufficient Assumption

The one idea it tests

Evidence measures one part, and the conclusion is about the size of the whole. The magic key ties the part's size to the whole's size.

The basic logic

Find the new idea in the conclusion that the premises never mention (overall size), and the old idea in the premises (the part's size). The answer that clicks says the two always move together, so smaller part guarantees smaller whole.

Tiny words that decide it

“provided that”
“always”
“proportional”

Playground logic

Lulu's patty is that the other class's shoes in the cubbies are smaller. Her top bun says those kids are shorter. The magic key is that shoe size always tracks height; plug that in and the conclusion clicks shut.

Step 2 · The kid story

Lulu Measures the Cubbies

Lulu noticed something at the shoe cubbies. "The sneakers from Mr. Park's class are smaller than ours, about a whole size smaller." Marcus folded his arms. "So what?" "So Mr. Park's kids must be shorter than us," Lulu said, "if these shoes are typical." Priya sipped her juice box. "That only works if one more thing is true." Lulu frowned at her clipboard. "That nobody wears giant boots?" "Closer. You need shoe size and height to go together, every time. Bigger feet, taller kid. Smaller feet, shorter kid." Lulu wrote it down: Magic key: shoe size always matches height. Then she added: Check Kevin. Kevin wore huge dinosaur slippers and was the shortest kid in the room. The magic key was not true in real life, but it would make the argument click.

Step 3 · Try the model question

Lulu: The sneakers in the cubbies for Mr. Park's class are smaller, on the whole, than the sneakers in our class's cubbies. So, as long as those sneakers are typical of each class, the kids in Mr. Park's class are shorter on average than the kids in our class.

Which one of these, if assumed, makes Lulu's conclusion follow logically?

Step 4 · The courtroom tale

The Case of the Short Shadows

In a fictional contest over who grew the tallest sunflowers, a gardener presented photos of shadows. "Your Honor, my rival's sunflowers cast shorter shadows than mine. So his sunflowers are shorter." Judge Reyes peered at the photos. "Counsel, what makes the shadows tell us about the flowers?" Mr. Whitfield, for the rival, smiled. "Exactly, Your Honor. That only works if the shadows were measured at the same hour, so a shadow's length always matches the flower's height." The gardener's lawyer nodded slowly. "If we prove that, does our case click?" "It would," said the judge. "Without it, you have measured the shadows, not the sunflowers."

Step 5 · Work the real question

Open PrepTest 124, Section 2, Question 22 in your official copy from LSAC (for example in LawHub) and read it there.

Your answer

How to apply it

Underline the measurement in the evidence and the bigger quantity in the conclusion. Notice the conclusion talks about something the evidence never touched. Look for the choice that welds the two together with a guarantee, so the measured thing always tracks the concluded thing. Test it: plug it in and see whether the conclusion is now forced. Ignore choices about variety, quirks, or unrelated features.