PrepTest 123, Section 2, Question 2
All Labrador retrievers bark a great deal.(26 more words not shown)
Which one of the following(15 more words not shown)
- AAll students who(27 more words not shown)
- BAll type A(39 more words not shown)
- CAll students at(42 more words not shown)
- DAll transcriptionists know(23 more words not shown)
- EAll of Kenisha's(48 more words not shown)
Reading the argument
These aren't Labs. They aren't St. Bernards. They're mixed breeds.
We know how much the two breeds bark separately. Labs bark a lot; St. Bernards bark infrequently—not very often. But why should crossing them give us dogs that bark a moderate amount? Nobody has told us how those traits combine.
Maybe the puppies bark as much as Labs. Maybe they're quiet like St. Bernards. Maybe their environment matters more than either parent's barking. Those are possibilities, not new facts about dogs. They show why we can't calculate “moderate” just by putting the two descriptions next to each other.
The question wants the same mistake in another argument. I'd try making up a parallel before reading the choices: imagine one kind of giraffe is brown and another is white. Does crossing them guarantee an offspring with a color halfway between the two? Not unless we know how the coloring is inherited. We can't assume the parents work like two paints we're mixing.
What we’re looking for
So look for two groups with contrasting properties, a combination of the groups, and an unsupported claim that the combination falls in the middle. All three pieces matter. An answer can mention a moderate result and still fail to match how the argument gets there.
Working the answers
- A
Where are the two extremes? Diligent students get good grades, and some students who aren't diligent also get good grades. Both premises give us good grades. Jane's somewhat good grades sound moderate, but the premises don't set up opposite outcomes that are then combined. That misses the contrast between frequent and infrequent barking.
- BCorrect
Type A chemicals are extremely toxic, corresponding to the Labs that bark a lot. Type B chemicals are nontoxic, corresponding to the St. Bernards that bark infrequently. The cleaner combines the two types, just as the dogs combine the two breeds.
Then comes the same unsupported middle result: the cleaner must be moderately toxic. Why? The answer never tells us what mixing these chemicals does to their toxicity. The mixture could still be extremely toxic. Knowing the properties of the separate ingredients doesn't establish the claimed property of their combination.
- C
This tells us that the family has members in both counties, not that the family ends up somewhere halfway between them. Members attending Hanson must live in Green County; members attending Edwards must live in Winn County. The conclusion follows from those facts. It neither makes our mistake nor predicts a moderate result.
- D
Bob's two jobs are associated with two skills, and the conclusion gives him both skills. It doesn't predict an intermediate skill or a moderate amount of either skill. Focus on that structural difference: the original averages the two properties; D combines them without averaging them.
- E
The well-made and badly made dresses give us a contrast, but then the argument changes direction. It uses the dresses' quality to decide who owns them. To match the dogs, we'd need a claim about a combination producing moderate quality.
E has a different problem: a well-made dress could belong to someone other than Kenisha. Knowing that her dresses are well made doesn't establish that every well-made dress is hers. That mistake about ownership isn't the unsupported averaging we're looking for.
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