Logical Reasoning · Sufficient Assumption

PrepTest 117 · Section 2 · Question 13

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 conclusion about one big group follows only if that group fits inside the part of the chain the premises cover.

The basic logic

Map the chain: problems of a certain kind can be fixed only by a change, and that change happens only if a reward is there. The conclusion talks about a group the premises never fully cover. The magic key says that group mostly falls inside the covered kind. Run the Click Test: add the choice and see if the conclusion locks shut.

Tiny words that decide it

“only”
“only if”
“unless”
“few”

Playground logic

Priya's chain: any mess Biscuit did not make gets fixed only if kids change habits, and kids change habits only if there is a reward. The top bun is about big messes in general. The magic key: few big messes are Biscuit's doing, so the chain covers almost all of them.

Step 2 · The kid story

The Reward Chart

The house was a disaster. Socks on the stairs. Crumbs on the couch. Grandpa called a family meeting. Priya, visiting for the afternoon, drew a chain on the fridge whiteboard. "Any mess that Biscuit did not make can only be fixed if you kids change your habits. And you only change your habits if there's a reward." Tommy nodded. "True. Very true." "So," said Priya, "few of the big messes will get fixed unless there's a reward chart." Lulu raised her hand. "Wait. What if most of the big messes are Biscuit's? Then your chain doesn't reach them." Everyone looked at Biscuit. Biscuit looked at a chewed shoe. "Fine," said Priya. "I'm assuming few big messes are Biscuit's." Lulu wrote that down.

Step 3 · Try the model question

Priya: Any mess not made by Biscuit can be fixed only if the kids change their habits. The kids will change their habits only if there is a reward. So few of the big messes in the house will be fixed unless there is a reward.

Which added assumption would make Priya's conclusion come out airtight?

Step 4 · The courtroom tale

The Leaky Roof Hearing

A city council was sued by a neighborhood group. The council's lawyer argued: "Any leak not caused by storms can be fixed only by new roofing. New roofing happens only if residents get a tax break. So few of the major leaks in town will be fixed without a tax break." Mr. Whitfield raised a finger. "Your Honor, the chain only covers leaks not caused by storms. What if most major leaks come from storms? Then the chain says nothing about them." The lawyer coughed. "Our engineers found few major leaks come from storms." Mr. Whitfield smiled. "Then say so. That is the missing link." The judge wrote it in big letters.

Step 5 · Work the real question

Open PrepTest 117, Section 2, Question 13 in your official copy from LSAC (for example in LawHub) and read it there.

Your answer

How to apply it

Diagram the premises as a chain of 'only' links. Then compare the group in the conclusion with the group the chain covers. Spot the gap: the conclusion talks about a group the premises only partly reach. Look for the choice that places that group inside the covered part. Click Test each choice; reject any that reverses an 'only if' or adds facts the chain never uses.