Sufficient & Necessary Questions - - Question 38

If the economy is weak, then prices remain constant although unemployment rises. But unemployment rises only if inve...

hmb891 April 7, 2020

Please do a video explanation to this question. I don’t understand how to do it!

I am unclear that if the unemployment is not rising than the economy is not weak. So with E, it must be false because BOTH the unemployment is not rising and the economy is not weak.

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Skylar April 13, 2020

@hmb891, we are currently working on uploading more video content, but I'm happy to help explain this question in writing for now.

First, let's break down the passage:
"If the economy is weak, then prices remain constant although unemployment rises."
We can diagram this as: Economy weak -> Prices constant & Unemployment rises
The contrapositive is: Prices not constant OR Unemployment not rising -> Economy not weak

"But unemployment rises only if investment decreases."
We can diagram this as: Unemployment rises -> Investment decreases
The contrapositive is: Investment not decreasing -> Unemployment not rising

"Investment is not decreasing."
This is the Sufficient condition of the contrapositive of the second sentence.
We can make the following chain using the contrapositives of the second and first sentences:
Investment not decreasing -> Unemployment not rising -> Economy not weak

Therefore, we can conclude that the economy is not weak.

(A) "Either the economy is weak or investment is decreasing" must be false. Our chain tells us both that investment is not decreasing and the economy is not weak. Therefore, nothing in (A) could be true. Since we are looking for the option choice that must be false, this is correct.

(E) states "either unemployment is rising or the economy is not weak." Our chain tells us that the economy is not weak. Since this is an option in (E), this answer choice could be true. Moreover, our first sentence tells us says: Economy weak -> Unemployment rises. The contrapositive of this is: Unemployment not rising -> Economy not weak. So, the scenario results in either unemployment rising or the economy not being weak. If one of the options in (E) is not true, the other will be. So, (E) is incorrect because it does not have to be false.

Does that make sense? Please let us know if you have any other questions!