To get the free dessert, one must order an entree and a salad. But anyone who orders either an entree or a salad can ...

Gabriela_Martinez on September 10, 2019

Difference between C and E.

I was about to pick C but I felt E had the same logical reasoning but more claim to being the correct answer since it is also about food items bought in pairs. Please explain.

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Irina on September 10, 2019


This a method of reasoning question, meaning it is more important to focus on the structure of the argument rather than its substance. Hence, an answer choice using similar context, e.g. food items bought in pairs, is usually a red herring. But let's look at the structure of the argument and compare it to (C) and (E).

The argument says to get a free desert (A), one must order entree (B) and a salad (C).

A -> B & C.

But anyone who orders entree (B) or a salad (C), can receive a free drink (D).

B v C -> D

We can infer that if one cannot get a free drink, it is because they either did not order a salad or an entree.

~D -> ~ (B & C)

Thus anyone who is not eligible for free drink (D) is not eligible for desert (A).

~D -> ~ A

Let's compare it to (C):

To grow azaleas (A), one needs soil rich in humus (B) and low in acidity (C)

A- > B &C

Anyone who has soil rich in humus (B) or low in acidity (C) can grow blueberries (D)
B v C -> D

~ D -> ~(B&C)

So anyone who cannot grow blueberries(D) cannot grow azaleas (A).

~D -> ~A

As we can see, (C) is identical to the stimulus.

Let's look at (E):

To get a discount on ice cream (A), one must buy frozen raspberries and ice cream together (B & C)

A -> B &C

Anyone who buys ice cream (C) or raspberries (B) will get a coupon (D)

B v C - > D

So anyone who does not get a discount (A) will not get a coupon (D)

~A -> ~D

This is a flawed argument, and the conclusion is reversed compared to the stimulus, hence we can eliminate (E) as the correct answer.

Let me know if you have any further questions.

davealts on November 10, 2019

it's not really identical though because in the stimulus they have one of the conditions only to conclude something. The blueberries have both of the conditions. Thats what led me to pick E even though it doesn't make sense.

shunhe on January 3, 2020


I'm not really sure what you mean by "the blueberries have both of the conditions" and "in the stimulus they have one of the conditions only to conclude something." Could you elaborate? I'll try diagramming the question and answer again in a more compact form, and maybe this will clear up some confusions. First, I'll diagram the stimulus.

Free dessert - > Entree & Salad
Entree v Salad - > Free soft drink
Conclusion: ~Free soft drink - > ~Free dessert

So if A = free dessert, B = Entree, C = Salad, and D = free soft drink:

A - > B & C
B v C - > D
Conclusion: ~D - > ~A

We can diagram the answer choice as follows:

Grow good azaleas - > (soil is) rich in humus & (soil is) low in acidity
Rich in humus v Low in acidity - > Grow blueberries
Conclusion: ~Grow blueberries - > ~Grow good azaleas

And we can see that if A = grow good azaleas, B = rich in humus, C = low in acidity, and D = grow blueberries, then the structure of this answer choice matches that of the stimulus, and so (C) is the correct answer choice. Hope this helps, and feel free to ask any further questions if it still doesn't make sense.