Q25 - To get the free dessert

[ManhattanPrepLSAT1]

The reason why answer choice (B) is wrong is because the conclusion of (B) does not match. It should have said, "if someone has nothing better to do, then that person will not be elected class president."

~BTD ---> ~ECP

Notation: BTD = something better to do, ECP = elected class president

Instead we were given, "if someone has something better to do, then that person will not be elected class president."

BTD ---> ~ECP

Clearly not the same relationship, though tough to spot. Let me run through the whole question though real quick.

We're looking for the following pattern:

D ---> E + S
E or S ---> Soft drink
------------------------
~Soft drink ---> ~D

Notation: D = dessert, E = entree, S = Salad

(A) wrong for many reasons, but the second premise should have contained an "or" and should have had the terms university diploma and sales experience in sufficient condition.
(B) conclusion has the wrong claim as described above.
(D) should have had an "and" in the first premise.
(E) reverses the conclusion. Should have said, "anyone who will not get the coupon, will not get a discount."

Hope that helps!


#officialexplanation

[zainrizvi]

Why is (B) wrong? It seems very similar to (C). Is it because of the "want" instead of "can"?

[rebecca.arian]

Can someone please explain to me the difference between C and E in this question?

[ManhattanPrepLSAT1]

Answer choices (C) and (E) are similar, but while answer choice (C) matches the reasoning in the stimulus, answer choice (E) reverses the conclusion.

In a simpler form, imagine the stimulus says

F ---> G
G ---> H
---------
~H --> ~F

That's a good argument using contrapositive argument structure.

Answer choice (C) here is essentially:

R ---> S
S ---> T
---------
~T ---> ~R

Another good argument that uses contrapositve argument structure - a match!

Answer choice (E), however, is more like:

K ---> L
L ---> M
---------
~K ---> ~M

This is a negation of the logic, and the conclusion also reversed the logic to read ~M ---> ~K, then it would have been a contrapositive and match for the reasoning.

Make sense?

[T.J.]

There is another point that I want to bring up.

The task here is to match the argument. The one given is a valid argument whereas (B) is not for the reason that any class president actually needs to have something better to do (the necessary condition of being a president).

In this aspect, we can sweep out (B)

[ManhattanPrepLSAT1]

Great point T.J.

[andrewgong01]

"B" seems a bit like a paradox but I can't fully work out why on what the logic behind "B" is that allows for a "paradox" ; it just seems strange as I dissect this choice further between "C" and "B"

B's Argument:

[1]Elect President -> Well Liked+ Well known. Contrapositive: If you are either not well liked or not well known then you can not be elected as president

[2]Well known or well liked --> something better to do Contrapositive: If you have nothing better to do you are neither well known nor well liked

[3]THUS if you do not have anything better to do you will not be elected as a president (this is the proper conclusion; not the actual conclusion the argument stated ) --This is the contrapositive of the two premises By this chain of logic, If you are elected as president, then you have nothing better to do.

BUT if you have nothing better to do then you are neither well known nor well liked (from [2]) and hence you fail the requirements to be elected president given by [1] . Then no one can be elected president because those who are well liked and well known are not going to be president either.

[ohthatpatrick]

Is this an easier way to think about it?

ORIGINAL
Prem: Free dessert ---> entree/salad --> free soft drink
Conc: ~free soft drink --> ~Free dessert

(B)
Prem: Elected Pres --> well liked / well known --> something better to do
Conc: something better to do --> ~Elected Pres

It's almost the same,
but they forgot to put a "not" in front of "something better to do".

Every time you see "No A's are B's", you should translate that as "All A's are ~B's"

[BenF939]

In this question, I thought the either/or language indicated the special conditional relationship to always make sure one of those is selected.

Why was the either/or in the second sentence of the entree problem diagrammed using the traditional "or" for multiple conditional statements?