Logical Reasoning · Paradox

PrepTest 129 · Section 2 · Question 3

Phase 1 (your first ~400 questions): read the guidance, then answer. No clock.

Step 1 · Pre-Question Guidance · read this first

Question type

Paradox

The one idea it tests

Every individual piece goes up, yet the group average goes down; find the fact that makes both true.

The basic logic

An average depends on WHO is still in the group. If the mix of members changes over time, the average can fall even while each member rises. Look for an answer that changes the mix of the group, and check that it explains both sides of the surprise.

Tiny words that decide it

“each”
“average”
“nonetheless”

Playground logic

Every kid in the reading club reads a few more pages each week, but the club's average pages per report still drops by the end. The handshake: the three biggest readers finished the challenge early and stopped reporting, so only the lighter readers were left in the average.

Step 2 · The kid story

The Shrinking Reading Average

Ms. Rivera started a ten-week reading club. The rule: each week, every kid must read a few more pages than the week before. Kevin read about dinosaurs, then more about dinosaurs, then a little more about dinosaurs. Everyone's pages crept up every single week. But in week ten, Ms. Rivera looked at the chart. "Hmm. The average pages per report is lower than it was in week one." Marcus jumped up. "Someone is cheating! Detective Marcus is on the case!" Priya calmly flipped through the folder. "Nadia, Owen, and Sharon read the most pages. They finished the whole challenge by week six and stopped turning in reports." Lulu nodded. "So the big readers left the average, and only the smaller readers stayed in it." Marcus sat down slowly.

Step 3 · Try the model question

In a ten-week reading club, every member read a few more pages each week than the week before. Nonetheless, by week ten, the average number of pages per weekly report was lower than at the start.

Which one of these, if true, best explains the surprising result?

Step 4 · The courtroom tale

The Case of the Falling Bake Sale

Judge Okafor frowned at the poster. "Every baker raised their cookie price a little each week. Yet the average price per cookie sold went down. Fraud?" Mr. Whitfield smiled. "No, Your Honor. Exhibit B: the two bakers selling the fanciest, priciest cookies sold out and closed their tables in week three." "So after that..." "After that, Your Honor, only the bakers with cheap cookies were left. Each of them kept raising prices, just as promised. But the average counts only who is still selling." The judge set down her gavel. "Every price up, average down, and nobody lied. Case dismissed. Pass the snickerdoodles."

Step 5 · Work the real question

Open PrepTest 129, Section 2, Question 3 in your official copy from LSAC (for example in LawHub) and read it there.

Your answer

How to apply it

State both sides of the surprise in your own words: each piece rises, yet the average falls. Ask what could change the group behind the average over time. Test each choice: does it make BOTH facts true at once? Drop choices about things outside the group being averaged, choices that only explain one side, and choices that merely make the puzzle feel smaller.