PrepTest 119, Section 3, Question 25
False chicory's taproot is always one half as(44 more words not shown)
If the statements above are(11 more words not shown)
- AIf two false(29 more words not shown)
- BIf a false(24 more words not shown)
- CIt is not(24 more words not shown)
- DIf the plants(29 more words not shown)
- EIf a false(29 more words not shown)
Reading the argument
The root is always half the plant's height. So if one of these plants is taller, its root must be longer too. A fixed proportion lets us carry information about height over to root length.
The rainfall claims have different strengths. More rain generally means more height, but that is described as a tendency. Then we get a definite rule: a plant receiving more than twice the habitat's average rainfall always reaches above-average height. Link that guaranteed height to the root proportion, and we get a guaranteed longer-than-average root.
What we’re looking for
That's the prediction for the must-be-true question. Start with the stated rainfall condition, get the height, then get the root length. Don't work backward from a tall plant and decide how it became tall. Rain may be one influence without being the only way to exceed the average.
Working the answers
- A
Shorter than another plant doesn't mean below average. Both plants could be unusually tall, with one still taller than the other. They could both have received more than twice the average rainfall. We have no basis for concluding that the shorter-rooted plant probably falls below that rainfall threshold.
- B
A longer-than-average root does tell us the plant is taller than average. But it doesn't identify the cause of that height. Perhaps other growing conditions or the plant's own characteristics helped it grow tall. Those are possibilities the passage leaves open. The high-rainfall condition guarantees height; height doesn't establish that particular amount of rain, even as a stated likelihood.
- C
This rules out a possibility the passage never excludes. A plant could receive average rainfall and still grow taller than average for some other reason. Saying that especially high rainfall guarantees above-average height doesn't make that much rain the only possible route to such height.
- D
Equal or lower height doesn't establish equal rainfall. The general rain-height relationship is a tendency, not a rule saying that rainfall alone determines each plant's exact height. Differences in other conditions could affect the result. We cannot read a precise rainfall comparison backward from the groups' heights.
- ECorrect
More than twice the average rainfall guarantees above-average height. Since the taproot is always half the plant's height, that plant must also have a longer taproot than an average-sized plant.
For example, if average height were 20 centimeters, an average-sized plant's root would be 10 centimeters. A plant guaranteed to exceed 20 centimeters would have a root exceeding 10. These are illustrative numbers; the same relationship holds whatever the actual average height is.
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