LSAT 133 | Section 1 | Logical Reasoning: Q21

LR Question 21 Explanation

QUESTION TEXT: On the Discount Phone line, any domestic long-distance…

QUESTION TYPE: Parallel Reasoning

CONCLUSION: Any domestic long distance phone call that does not cost 15 cents per minute costs 10 cents per minute.

REASONING: If a domestic phone call is placed between 9–5 then it costs 15 cents. Any other domestic long distance call costs 10 cents.

ANALYSIS: This is a good argument. There are only two types of phone calls: 15 cent and 10 cent calls. So if one doesn’t cost 15 cents then it must cost 10 cents.

The structure is: If it isn’t one then it must be the other.

The answer choices all use similar words but have different structures. If a class has lab work, it will be in a lab. Otherwise it will be in a normal class.

To properly match the “if not one then the other” structure, the correct answer must say that if the class isn’t in one room then it is in the nother.

___________

1. This is close, but the conclusion should have said the class will be conducted in a normal classroom.
2. This should conclude that a class will be held in a lab if it isn’t in a normal classroom.
3. This does not match the structure, which was: If not one, then it must be the other.
4. This should have said that if it was in a lab then it wouldn’t be in a normal classroom. Using “extensive lab work” as the sufficient condition introduces a new element into the structure.
5. CORRECT. Here we go. If it isn’t in one (a normal classroom) then it is in the other (a lab)