PrepTest 133, Section 1, Question 21
On the Discount Phoneline, any domestic long-distance call(45 more words not shown)
The pattern of reasoning in(15 more words not shown)
- AIf a university(41 more words not shown)
- BIf a university(40 more words not shown)
- CIf a university(41 more words not shown)
- DIf a university(40 more words not shown)
- EIf a university(41 more words not shown)
Reading the argument
There are only two possible rates here. If the call doesn't cost ten cents a minute, it has to cost fifteen.
The time rule covers every domestic long-distance call on this service. A call either starts between nine and five or it doesn't. Calls in the first group cost fifteen cents; all the others cost ten. Ruling out the ten-cent rate therefore leaves the fifteen-cent rate. This reasoning works.
But 'there are two possibilities' is too vague for the parallel question. We need to track which pieces the conclusion connects. It starts by ruling out one result—the ten-cent rate—and ends by affirming the other result—the fifteen-cent rate. It doesn't merely tell us when the call started.
What we’re looking for
All five choices use the same setup. Extensive lab work plays the role of starting between nine and five. A laboratory is the fifteen-cent result; a normal classroom is the ten-cent result. So we're looking for: not in a normal classroom, therefore in a laboratory. Keep those roles straight even though every choice uses nearly identical words.
Working the answers
- A
This starts with a class that doesn't involve extensive lab work and concludes that it won't be in a laboratory. In the phone argument, that would be starting outside the nine-to-five period and concluding that the call won't cost fifteen cents. The original instead starts by ruling out the ten-cent price and concludes that the fifteen-cent price applies. A changes both the starting point and the form of the result.
- B
This has the right starting point: the class isn't in a normal classroom, matching a call that doesn't cost ten cents. But it ends with the wrong piece: the class involves extensive lab work. That would correspond to concluding that the call started between nine and five. That may be a step along the way, but our argument goes on to establish the other price. We need the laboratory as the conclusion.
- C
This begins with a class in a normal classroom and concludes it isn't in a laboratory. That corresponds to starting with a ten-cent call and concluding that it isn't a fifteen-cent call. The original starts with not ten and concludes fifteen. C uses the opposite starting information and a negative conclusion rather than the positive remaining option.
- D
This begins with extensive lab work and concludes that the class isn't in a normal classroom. That would match a call starting between nine and five and therefore not costing ten cents. Again, the original begins with a price being ruled out, not with the initial time condition, and ends by naming the other price.
- ECorrect
The class isn't in a normal classroom, so it must be in a laboratory. Those locations match the two rates: not the ten-cent option, therefore the fifteen-cent option. The shared premises cover classes with extensive lab work and all other classes, just as the original covers calls in the stated time window and all other calls. Both arguments eliminate one result to establish the other.
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