16Hit1600
Information and IdeasVery hardInferring a hidden variable behind an anomaly

Information and Ideas practice question

Every time paper fiber is pulped and re-formed into a sheet, the individual fibers break a little shorter, and shorter fibers bond less tightly, producing weaker paper. A mill that blends recycled fiber with fresh wood pulp therefore logs the recycled fraction of each batch, expecting strength to fall as that fraction rises. Most of its records match, but two do not: a batch of 55 percent recycled content tested stronger than a batch of 30 percent. Investigating, the mill found that the recycled fiber in the 55 percent batch had come entirely from office paper newly collected from a single downtown employer, while the 30 percent batch drew on the mill's usual mixed municipal stream. This finding suggests that ______

Which choice most logically completes the text?

  1. A. how many previous pulping cycles a batch's recycled fiber has undergone can matter as much to the batch's strength as the size of the recycled fraction does.Correct
  2. B. the mill's recycled fraction figures are of no use in anticipating the strength of a batch.
  3. C. recycled office paper yields stronger sheets than fresh wood pulp does.
  4. D. the fiber in the mill's usual municipal stream has been pulped so often that it can no longer be blended into usable paper.

Answer: A. how many previous pulping cycles a batch's recycled fiber has undergone can matter as much to the batch's strength as the size of the recycled fraction does.

The passage supplies the mechanism—strength depends on fiber length, which shortens with each pulping—and an anomaly in which a higher-recycled batch was stronger, differing only in the history of its recycled fiber. The reasonable conclusion is that number of prior cycles is a second, potentially decisive variable. B overcorrects: the text says most records do follow the expected pattern, so the fraction remains informative. C reverses the stated mechanism; nothing suggests recycled fiber outperforms virgin pulp, only that once-cycled fiber outperforms much-cycled fiber. D is far too strong—the mill is currently making paper from that stream, and only relative weakness, not unusability, is described.

Why the other answers are wrong

B. the mill's recycled fraction figures are of no use in anticipating the strength of a batch.
Most of the mill's records did match the expected pattern — only two didn't — so the recycled fraction still carries useful information about strength.
C. recycled office paper yields stronger sheets than fresh wood pulp does.
Nothing in the passage says recycled fiber beats fresh pulp; the comparison is between once-pulped office paper and much-pulped municipal fiber, and the stated mechanism is that every pulping cycle weakens fiber.
D. the fiber in the mill's usual municipal stream has been pulped so often that it can no longer be blended into usable paper.
The mill is still making paper from the municipal stream, and the 30 percent batch was only weaker than expected — the passage never suggests that fiber is unusable.

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