PrepTest 116 · Section 3 · Question 22 (Parallel Flaw)

Step 1 · Pre-Question Guidance · read this first

Question type

Parallel Flaw

The one idea it tests

Two 'most' statements chained together do not produce a third 'most'.

The basic logic

X-Ray the argument: Most A are B. Most C are A. So most C are B. The flaw is that the C's who are A might be exactly the A's who are not B, so the two 'mosts' may barely overlap. Find the answer with the same skeleton: two mosts, linked through a middle group, concluding a most.

Tiny words that decide it

“most”
“therefore”
“most”
“most”

Playground logic

The patties are two 'most' facts: most dog walkers wear sneakers, and most kids on one street walk dogs. The top bun claims most kids on that street wear sneakers. The X-Ray shows a chain of two mosts, and mosts do not chain.

Step 2 · The kid story

The Sneaker Survey

Marcus is doing a detective survey. 'Fact one: most kids who walk a dog every morning wear sneakers to school. Fact two: most kids on Maple Street walk a dog every morning. Therefore, most kids on Maple Street wear sneakers. Boom.' Priya sips her juice box. 'Picture it. Say there are ten dog walkers in town, and seven wear sneakers. Maple Street has four kids, and three of them walk dogs. But what if those three are among the walkers who wear rain boots?' Marcus blinks. 'Then only one Maple kid might wear sneakers.' 'Right,' says Priya. 'Two mosts can miss each other. You need them to overlap, and you never showed that.' Lulu draws two circles on her clipboard that barely touch.

Step 3 · Try the model question

Most kids who walk a dog every morning wear sneakers to school. Most kids on Maple Street walk a dog every morning. So most kids on Maple Street wear sneakers to school.

Which one of the following contains reasoning that goes wrong in the same way as the reasoning above?

Step 4 · The courtroom tale

The Paint Store Puzzle

In a fictional trial about a missing ladder, the prosecutor reasons: 'Most people who buy blue paint live on Elm Road. Most customers in the store that afternoon bought blue paint. So most of that afternoon's customers live on Elm Road, near the ladder!' Mr. Whitfield sketches two circles on a pad. 'Your Honor, the afternoon's blue paint buyers could all be from the small group who live elsewhere. Two mosts do not guarantee a most. They might overlap a lot, or hardly at all.' The judge squints at the circles. 'The prosecution needs actual addresses, not a chain of mosts.' The ladder, it turns out, was in the store's back room the whole time.

Step 5 · Work the real question

Open PrepTest 116, Section 3, Question 22 in your official copy from LSAC (for example in LawHub) and read it there.

Your answer

How to apply it

X-Ray the original with letters: write each claim as most A are B, most C are A, conclusion most C are B. Ignore the topic entirely. Then letter-code each answer. Throw out any that use 'all' or 'only' in ways that make the logic valid, and any with some other flaw. Keep the one whose two premises are both 'most' statements linked through a middle group, ending in a 'most' conclusion.