PrepTest 151 · Section 2 · Question 23 (Parallel Flaw)

Step 1 · Pre-Question Guidance · read this first

Question type

Parallel Flaw

The one idea it tests

Being stronger one unit at a time does not make the whole bunch stronger, because the bunch might hold fewer units.

The basic logic

X-Ray the flaw: each piece of X beats each piece of Y, so a thing made of X beats a thing made of Y. It ignores how many pieces each one holds. Find the answer that makes the same per-piece to whole jump.

Tiny words that decide it

“each”
“much more”
“so”
“must”

Playground logic

Ms. Rivera says one new bulb is much brighter than one old bulb, so the art room (new bulbs) must be brighter than the gym (old bulbs). That is a Bad Comparison: it forgets that the gym might have fifty bulbs and the art room only two.

Step 2 · The kid story

The Bright Idea

The school swaps the old light bulbs in the art room for new ones. One new bulb is much brighter than one old bulb. The gym still uses old bulbs, and it is plenty bright. Marcus declares, "So the art room must be even brighter than the gym! We will all need sunglasses in art class." Kevin starts drawing a dinosaur in sunglasses. Lulu counts on her clipboard. "The gym has forty bulbs. The art room has three." Marcus blinks. "Oh." Priya sips her juice box. "Each new bulb wins, Marcus. But a room's brightness depends on how many bulbs it has too. You compared one to one and then jumped to the whole room."

Step 3 · Try the model question

One new bulb is much brighter than one old bulb. The gym is lit by old bulbs and is bright, so the art room, lit by new bulbs, must be even brighter. Kids in art class will soon want sunglasses.

Which choice makes the mistake most like the one above?

Step 4 · The courtroom tale

The Case of the Heavier Truck

Two moving companies argue over a weight fine. "Your Honor," says one lawyer, "each of our boxes holds feathers. Each of their boxes holds bricks. A brick box is far heavier than a feather box. So their truck must be heavier than ours." Mr. Whitfield stands, hooks his thumbs in his suspenders, and asks a single question. "How many boxes were on each truck?" The driver mumbles, "We had two hundred. They had four." The judge sets down her pen. "Counselor, you compared one box to one box, then jumped to the whole truck. The count matters."

Step 5 · Work the real question

Open PrepTest 151, Section 2, Question 23 in your official copy from LSAC (for example in LawHub) and read it there.

Your answer

How to apply it

Name the flaw in plain terms first: a per-piece comparison is used to judge the whole, without checking how many pieces there are. Then X-Ray each answer for that exact jump. An answer may share a topic or a feel and still have a different flaw, so ignore surface topic. The keeper compares single units and then concludes about totals while saying nothing about amounts.