Logical Reasoning · Sufficient Assumption

PrepTest 110 · Section 2 · Question 2

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

A rule says do whatever achieves a goal; the conclusion names one specific item. The magic key links that item to the goal.

The basic logic

The patty connects a goal to a rule (always do what serves the goal). The top bun says we need one particular thing. Nothing yet says that thing is required for the goal. Find the answer that makes the thing a must-have for the goal, and the argument clicks shut.

Tiny words that decide it

“always”
“needs”
“so”
“required”

Playground logic

Ms. Rivera's rule says the class should always do what is good for reading, and a cozy reading corner is good for reading. Tommy concludes the class needs new beanbags. The magic key is that new beanbags are required for a cozy reading corner; with that in place, the Click Test passes.

Step 2 · The kid story

Tommy and the Beanbag Campaign

Tommy really wanted new beanbags. He made a speech to the class. "Fact one: a cozy reading corner helps kids read. Fact two: Ms. Rivera always says we should do whatever helps kids read. So the class needs new beanbags!" Everyone clapped, mostly because Tommy bowed. Lulu raised her clipboard. "Wait. You proved we need a cozy corner. You did not prove we need beanbags. Maybe a rug and some pillows would make it cozy." Tommy frowned. Priya helped him. "Tommy, you need one more brick. Say that you cannot have a cozy corner without new beanbags. Then the beanbags are part of what helps kids read, and the rule says do it." Tommy added the sentence. Lulu checked the chain link by link. Click. "Now it works," she said. Biscuit, who was visiting, lay down on the old rug anyway.

Step 3 · Try the model question

Tommy: A cozy reading corner helps kids read. Our class should always do whatever helps kids read. So our class needs new beanbags.

Tommy's conclusion would be guaranteed if you added which sentence?

Step 4 · The courtroom tale

The Case of the Library Clock

A town rule says the library must always do what keeps visitors on schedule. A lawyer, Ms. Okafor, argued: "A clear clock on the wall keeps visitors on schedule. So the library must buy the giant brass clock from my client." Mr. Whitfield rose. "Your Honor, she has proved the library needs a clear clock. She has not proved it needs that brass clock. A cheap plastic one is perfectly clear." The judge turned to Ms. Okafor. "Can you show that only this brass clock can keep visitors on schedule?" She could not. "Then your chain is missing its last link," said the judge. "Case dismissed. Also, it is five past noon. Lunch."

Step 5 · Work the real question

Open PrepTest 110, Section 2, Question 2 in your official copy from LSAC (for example in LawHub) and read it there.

Your answer

How to apply it

Lay out the chain: a thing serves a goal, and a rule says always do what serves that goal. Then look at the conclusion and notice it names something more specific than the goal. Ask what single sentence would force that specific thing to be needed for the goal. Test each choice by plugging it in. Reject choices that only make the item helpful, affordable or nice, and watch for one that reverses the direction.