Reading Comprehension · Science
PrepTest 148 · Section 2 · Passage 4
Questions 20–27
Before you start
Open PrepTest 148, Section 2 in your official copy from LSAC and read the passage for Questions 20–27, using the structure guide below. The passage is not reprinted here.
Structure guide
- P1: introduces a popular practice, separates a clearly useful version from a doubtful one, and names the premise the doubtful one rests on
- P2: questions that premise, cites an expert's alternative view, and gives an everyday example
- P3: raises an objection to the critique and explains how the method actually works
- P4: shows why the method misleads, so the objection fails, and ends with a pointed question about why the premise is popular
Step 2 · The kid passage
Where Does the Giggle Live?
Lots of kids at our school now use the class sound meter to make pictures of what the class is doing. When the custodian uses it to find a rattling heater, it works like a flashlight: it just shows him where the rattle is. Nobody doubts that. But Marcus uses it for something very different. His project only works if one thing is true: that the class's mood splits into separate pieces (giggling, focusing, grumbling), and that each piece sits at its own table. Marcus calls this the Corner Idea.
Maybe moods don't split like that at all. Grandpa, who taught school for forty years, thinks giggling, focusing and grumbling are probably just sides of one big class mood spread over the whole room. You cannot say the art table is the home of giggles and the reading rug is the home of focus, the way Marcus's poster claims. When I giggle, it's usually about the book I'm reading!
But wait. If Grandpa is right, why do Marcus's maps show bright spots at just a few tables during joke time? Here's the trick. Marcus first records the room during quiet reading. Then he records it during joke time. Then he subtracts the first recording from the second, and only the leftover noise glows on his map.
The problem nobody mentions: the whole room is making noise both times. Subtracting hides all that spread-out noise, so the map looks neatly sorted when the room isn't. The maps sure look cool. But isn't the Corner Idea popular partly because those cool maps show it off so well?
Step 4 · The courtroom tale
The Case of the Glowing Garden Chart
In a made-up county, a gardener claimed only the fence-side beds used the new sprinkler water. His expert showed a chart where just those beds glowed. Mr. Whitfield tugged his suspenders. "Your Honor, how was this chart made?" The expert said, "We measured every bed before the sprinkler, then after, and subtracted." "So every bed got wet both times?" "Well, yes." "And your chart erased all that shared water and showed only the extra?" "Yes." Mr. Whitfield turned to the judge. "Your Honor, a picture of the leftover is not a picture of the whole. The neat glow comes from the subtraction, not from the garden. Maybe the chart is persuasive simply because it is pretty." The judge nodded slowly.