PrepTest 155 · Section 1 · Question 21 (Principle)

Step 1 · Pre-Question Guidance · read this first

Question type

Principle (apply)

The one idea it tests

Chain the rules carefully: one rule says when something is required, another says when something is forbidden. The right conclusion triggers each rule correctly and never runs one backwards.

The basic logic

Write each rule as an arrow. Rule one: if A or B, then C. Rule two: if D, then not A. Find the case whose facts trigger the arrows forward, and whose conclusion is exactly what the arrows deliver.

Tiny words that decide it

“if”
“or”
“should not”
“any”

Playground logic

Ms. Rivera's party rules are the patty. A table gets a tablecloth if it gets candles or if it is the guest table; no table by the windy window gets candles. Lulu's top bun: the guest table by the window gets a tablecloth but no candles, because both arrows fire forward.

Step 2 · The kid story

Ms. Rivera's Party Rules

Ms. Rivera taped rules to the board for the class party. "Any table with candles gets a tablecloth. The guest of honor table also gets a tablecloth. But no table next to the big open window gets candles. Too windy."

Marcus pointed. "Grandpa is the guest of honor, and his table is right by the window. So no tablecloth and no candles!"

Lulu checked her clipboard. "No. Guest table means tablecloth, no matter what. Window means no candles. So Grandpa gets a tablecloth and zero candles."

Kevin raised his hand. "Can the table by the door have candles?"

"The rules don't force it," Lulu said. "They only say what happens if it does."

Grandpa sat down at his tablecloth, very pleased, and blew out an imaginary candle.

Step 3 · Try the model question

Party rules: a table gets a tablecloth if it gets candles or if it is the guest of honor table. No table beside the open window may get candles.

Which judgment is most firmly backed by these rules?

Step 4 · The courtroom tale

The Town Pool Permit

The town code said a pool must have a fence if it has a diving board or if it sits at a public park. It also said no pool near the airport may have a diving board.

A builder wanted a park pool beside the airport with no fence. "No diving board allowed, so no fence needed," he argued.

Mr. Whitfield adjusted his suspenders. "Your Honor, the fence rule has two doors. The diving board is one. The park is the other. This pool walks through the park door."

The judge ruled: "Fence, yes. Diving board, no. Both rules point forward."

Step 5 · Work the real question

Open PrepTest 155, Section 1, Question 21 in your official copy from LSAC (for example in LawHub) and read it there.

Your answer

How to apply it

Turn each guideline into an arrow, noting which conditions require something and which forbid something. For each choice, list its facts and check which arrows they trigger, always going forward, never backward. Then compare the choice's conclusion to what the triggered arrows actually deliver. Eliminate choices that reverse an arrow, rely on a condition no rule mentions, or ignore a rule that their facts trigger. The survivor matches every rule its facts touch.