Q20 - If the majority of residents

[evelina.chang]

For this question, I'm confused why the correct answer is (D) instead of (B) - which is what I chose. My reasoning went something like this:

if the majority residents complain about ants (RCA) -> then there will be extermination services (ES)

However, the majority of the residents do not complain about ants (no RCA)-> so there will not be extermination services (no ES)

I thought that (B) was the most similar, because:

If airline collects higher airfares (HA)-> # of flights reduced (#ofFR)

However, the majority of people will not pay higher airfares (no HA) -> so the number of flights will not be reduced (no #ofFR).

Any help would be greatly appreciated! Thanks!

[ManhattanPrepLSAT1]

I thought that (B) was the most similar, because:

If airline collects higher airfares (HA)-> # of flights reduced (#ofFR)

However, the majority of people will not pay higher airfares (no HA) -> so the number of flights will not be reduced (no #ofFR).

It looks like you've fallen victim to another challenging interpretation of "unless." This idea is one of the most frequent sources of error when it comes to conditional logic on the LSAT. Answer choice (B) is actually a valid argument employing contrapositive argument structure.

Here's the stimulus:
MC ---> Ex
~MC
--------------
~Ex

Notation Key: MC - majority of residents complain, Ex - hire an exterminator

The error of reasoning is a common one - it commits a negation of a conditional statement.

Answer choice (D) also commits a negation of a conditional statement.

S ---> MEA
~S
-------------
~MEA

Notation Key: S - successful in getting a certain band, MEA - most employees will attend

Let's look at the incorrect answers:

(A)
FS ---> TC
FS
-------------
TC

Notation Key: FS - funds are sufficient, TC - theater constructed
This is positive argument structure and does not represent an error of reasoning.

(B)
R ---> HA
~HA
-------------
~R

Notation Key: R - flights reduced, HA - collect higher airfares
This is contrapositive argument structure and does not represent an error of reasoning.

(C)
SP ---> TC + M
M
----------------
SP

Notation Key: SP - start the project, TC - town council approves, M - mayor approves
This argument commits two errors in that it commits a reversal of a conditional relationship and fails to include one of the two necessary conditions. Neither of these errors matches that committed in the stimulus.

(E)
CC ---> SP or PC
~SP
-------------------
~CC

Notation Key: CC - dress code is changed, SP - school's principle approves, PC - parent council approves
This argument is close to valid, but it would need to have included the additional piece of information that the parent council will not approve the change - not the same error.

Hope that helps!