#20 - If the economy is weak, then prices remain constant

[Robert Carroll]

hifigirl,

Your diagram of the stimulus looks perfect!

Onto the answer choices:

In linking the contrapositive logic /ID --> /UR --> /EW, when investment is decreasing, the economy is NOT weak.

You diagrammed correctly but misspoke here - when investment is NOT decreasing, the economy is not weak. Your diagram proves that, and that's why answer choice (A) is correct.

UR --> ID but we know nothing else. Prices could remain constant as they are not linked to ID or UR.

All perfectly correct.

(C) MBT for same reasoning in (A)

Agreed, that's inferable by a valid chain.

EW --> PRC + UR allows for the economy to be weak AND prices to remain constant, if unemployment rate also decreases.

I think more should be said about this. The economy is definitely not weak. That's provable by the contrapositive of the chain. However, since that doesn't require prices to remain constant or otherwise, the second half of this answer could be true, making the entire "or" statement possible.

/PRC or /UR --> /EW allows for unemployment to rise AND economy to be not weak (if prices don't remain constant). It would hinge on activating the OR statement, suggesting /PRC --> /EW while unemployment rises.

We can more simply say that this answer must be true. The second element is definitely true, so the whole "or" is true.

Robert Carroll

[rm_reykjavik]

Hi! I see loads of people have diagrammed this out; my question is less about diagrams and more about how we should think about the stimulus. I initially noted that because investment is not decreasing, we can roughly take the contrapositive to be true (let me know if this looks good):

~ investment decreasing --> ~ unemployment increasing

~ (unemployment increasing AND prices staying constant) --> ~ economy weak

Answer A can be immediately selected because we know that both the economy is not weak AND investment is not decreasing (0,0) which means that "either ... or" is false.

However, I started to overthink the other answers.

For Answer B, I thought it was a bit weird that they were inserting a conditional relationship for two necessary clauses that had an 'AND' relationship. I figured that the 'AND' made them a biconditional (i.e. both must be true or false), which would make the conditional in one direction true. Ruled it out.

For Answer C, I saw it was a contrapositive. Ruled it out.

For Answer D, I began to wonder if it had the same problem as A. That is to say, it's possible that the economy could NOT be weak and prices are NOT the same (i.e. both necessary and sufficient condition are not met) .... This violates the 'either .... or' (0,) so why wouldn't this also be false?

For Answer E, it seems like we must have one or the other be true (or both could be true). Ruled it out.

Thank you!!!

[Amber Thomas]

Hi rm_reykjavic!

Your set-up with the contrapositives is absolutely correct! Since the necessary condition for Unemployment Rises isn't met, that means it cannot be true. If we don't have both Unemployment Rises AND Prices Remain Constant, we cannot have Economy Weak.

Economy Weak --> Prices Remain Constant AND (Unemployment Rises --> Investment Decreases)
(~Investment Decreases --> ~Unemployment Rises) OR ~Prices Remain Constant --> ~Economy Weak

Answer Choice A) You're correct! If Economy Weak, then Investment Decreasing must be true. However, we know that ~Investment Decreasing.

Answer Choice B) We don't know that this must be false, it could very well be true. We just don't have enough context to determine.

Answer Choice C) Exactly, this is a direct contrapositive.

Answer Choice D) For this choice, we know that the ~Economy Weak, since ~Investment Decreasing. So, the first half of the "or" statement is false. However, Prices Remain Constant could absolutely still be true. So, this statement remains potentially correct!

Answer Choice E) We know that since ~Investment Decreasing, ~Economy Weak, so this statement is accurate!

I hope this helps!