PrepTest 101 · Section 2 · Question 13 (Parallel Reasoning)

Step 1 · Pre-Question Guidance · read this first

Question type

Parallel Reasoning

The one idea it tests

Exactly two options, one is ruled out, so IF a pick is made from that set, it must be the other one.

The basic logic

X-Ray the skeleton: a source offers only two options; a reason knocks out option one; the conclusion is conditional: if the pick comes from this source, it is option two. The right answer copies all three pieces, including the 'if' in the conclusion and a real reason for eliminating one option.

Tiny words that decide it

“only two”
“so, if”
“the one”

Playground logic

The art cupboard holds just two glitter glues. Kevin's glue dried too fast to be the gold one. So if Kevin still takes all his glue from the cupboard, it was the silver one: two doors, one locked, and an 'if' on the conclusion.

Step 2 · The kid story

Kevin's Glitter Glue

The art cupboard holds exactly two glitter glues: gold and silver. Kevin only decorates with glitter glue. On Friday his dinosaur poster was dry in five minutes. 'It wasn't the gold,' Lulu said, checking her clipboard. 'Gold takes all afternoon to dry.' Marcus jumped up. 'So it was silver!' Priya held up her juice box like a gavel. 'Careful. Only if Kevin still takes all of his glue from the art cupboard. If he brought some from home, it could be any color.' Lulu wrote: two glues, gold is out, so IF it came from the cupboard, it's silver. Kevin added, 'Or it was magic dinosaur glue.' Everyone ignored Kevin.

Step 3 · Try the model question

The art cupboard holds only gold and silver glitter glue. Kevin uses only glitter glue, and the glue on his poster dried far too fast to be the gold. So if Kevin still takes all of his glue from the cupboard, he used the silver.

Which argument is most similar in its reasoning to the argument above?

Step 4 · The courtroom tale

The Two-Key Mystery

The museum guard testified that the vault has exactly two keys: a gold one and a silver one. Detective Moss added that the gold key was locked in the director's safe all night, so it could not have been used. Mr. Whitfield stood up for the prosecution. 'If the vault was opened with one of its own keys, Your Honor, it was the silver one.' Defense counsel objected. 'Maybe someone used a copy!' Mr. Whitfield nodded. 'That is why I said if. Two keys, gold is ruled out, so if a vault key was used, it was silver.' Judge Hale wrote in her notes: two choices, one eliminated, conditional conclusion.

Step 5 · Work the real question

Open PrepTest 101, Section 2, Question 13 in your official copy from LSAC (for example in LawHub) and read it there.

Your answer

How to apply it

X-Ray the stimulus into three pieces: a closed set of exactly two options, a reason that knocks out one, and a conclusion that names the other only under an 'if'. Write that skeleton down. Test each choice piece by piece. Cross off any whose conclusion is flat instead of conditional, any that knocks out both options, any where nothing really eliminates the first option, and any Matching Costume that only shares a surface look.