PrepTest 117, Section 2, Question 17
The tiny hummingbird weighs little, but its egg(59 more words not shown)
Which one of the following(8 more words not shown)
- AThe eggs of(12 more words not shown)
- BThe smaller and(20 more words not shown)
- CThe ratio of(24 more words not shown)
- DThe size of(21 more words not shown)
- EBird species vary(13 more words not shown)
Reading the argument
A big percentage of a tiny bird can still be a tiny egg. The hummingbird's egg weighs 15 percent as much as the adult bird. For the goose, it's about 4 percent; for the much larger ostrich, it's only 1.6 percent. The adults get larger while the eggs become smaller as a share of the adults' weight. That's a relative comparison, not a claim that hummingbirds lay heavier eggs than ostriches.
To see the difference, use made-up weights. An egg weighing 15 percent of a ten-unit bird would weigh 1.5 units. An egg weighing 4 percent of a hundred-unit bird would weigh four units. The second egg is heavier, even though it's a smaller percentage of its parent's weight. We don't need the actual weights to understand that those two comparisons can move in different directions.
What we’re looking for
The question asks which proposition these examples best illustrate. Three examples wouldn't prove a rule about every bird species, so keep the task in view: identify the pattern illustrated here. I'd look for the egg-to-adult weight ratio getting smaller as adult birds get larger.
Working the answers
- A
This compares the volume of an egg with its weight. The passage compares an egg's weight with the adult bird's weight. Those are different ratios. We haven't been given the egg volumes needed to make A's comparison, even though the passage mentions that the adult goose has greater volume than the hummingbird.
- B
This drops the relative part. A larger percentage of a small adult's weight doesn't establish a larger or heavier egg than a smaller percentage of a large adult's weight. The made-up numbers show why: 15 percent can describe a lighter egg than 4 percent when the adult weights differ. B turns a comparison of proportions into an unsupported comparison of actual egg sizes.
- CCorrect
The relevant ratio is egg weight divided by adult body weight. For the three birds, that ratio goes from 15 percent to 4 percent to 1.6 percent as adult size increases. C states that declining relative share. It captures the pattern the examples illustrate without confusing it with a ranking of actual egg weights.
- D
The passage doesn't tell us how the size of an egg affects the adult bird's eventual size. Describing two weights and their ratio doesn't establish a causal effect between them. D takes us from the observed comparison to a claim about development that the information doesn't address.
- E
We haven't been given the actual spread of egg sizes and adult sizes across species. The percentages compare each egg with its own adult, not the total variation in one set of sizes with the variation in another. E requires a different comparison from the one the examples provide.
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