#18 - Traffic engineers have increased the capacity of the

[Administrator]

Complete Question Explanation

Must Be True—SN. The correct answer choice is (B)

This conditional reasoning question appears more complex than it is due to the fact that the conditional language is all in the negated form. The question becomes much easier to work with if you take the contrapositive of the conditional statements, thus translating them from the negative into the positive. Conceptually, we can think about the conditional statements as attempting to tell us what is necessary for each sufficient condition to happen. Breaking down the language in the stimulus to the bare-bones idea in each statement will make any Sufficient-Necessary problem easier to manage.

Looking at the stimulus, we see a chain of conditional relationships. The increase in traffic flow required the city to make the investment in modeling technology. The resolution of the city’s financial predicament required the increase in traffic flow. We can note that the increase in traffic flow is the common term. We can diagram the relationship between both statements as follows:

• Resolution of financial predicament Increase in traffic flow City to make investment

Once we can see the simple chain, we are ready to turn to the answer choices.

Answer choice (A): Information unrelated to the conditional chain above is unlikely to be correct. In a Must Be True question, we are limited to what we know for certain from the facts in the stimulus. The stimulus provides no background on how the city decided on the particular modeling software used. The stimulus lacks information to support this answer choice.

Answer choice (B): This is the correct answer choice. This is the contrapositive of the conditional chain. If the city did not make an investment, the financial predicament would not have been resolved. This is because the resolution required the increased traffic flow, which in turn, required the investment.

Answer choice (C): From the stimulus, we know that the bridge can handle increase in rush-hour traffic flow. This answer choice does not limit itself to rush-hour; it states a fact about the day as a whole. We cannot draw any inference about the number of cars that cross the bridge in an average day, just about the short rush-hour periods. While this answer choice may seem likely to be true, and in fact could be true, remember that we are looking for the answer choice that must be true.

Answer choice (D): Like in answer choice (A), we do not have information about how the city made the decision to use the modeling software, or how the ultimate decision to go forward with the change to the bridge was made. Notice here that the unsupported portion of the answer choice was at the very end of the answer choice, and students who merely scan the answer choices or who are in a rush might miss the additional unsupported information.

Answer choice (E): Similar to answer choices (A) and (D), this answer choice is incorrect due to a lack of information. We do not know why the mayor supported getting the modeling software. We just know that he did purchase it. There could have been additional uses for the software.

[euniecho1]

Hello,

I found this problem very difficult to answer while taking the practice test #2, and I ended up getting it wrong. It has a lot of double negatives/"nots"... Could you please help me on how I can approach a question like this in the future? Thank you!!

(copy of question removed)


Best,
Eunie

[Adam Tyson]

Eunie, you're probably in good company being confused by all the negative language in this question. In fact, our published explanation of the question says as much and suggests using the contrapositives of each statement instead to make life a little easier.

That said, we can still deal with negation in conditional reasoning - we do it all the time when we create contrapositives. Take it step by step - first, look at each sentence and identify any conditional relationships. The first sentence has none, but the second sentence does, so start with the conditional indicator word "had" (which works like "if" and introduces a sufficient condition). The first part of that second sentence becomes:

Invested in Computer Modeling --> Increased Traffic Flow

Do the same with the next statement in that second sentence, focusing on the key indicator word "if", and you get:

Increased Traffic Flow --> Financial Problems Resolved

String those two together to make your conditional chain, and answer choice B turns out to be an easy leap from your first term to your last one.

Remember that when dealing with negative statements you can handle them one of two ways: 1) take the contrapositives and turn them into positive statements or 2) approach them very mechanically and diagram them with a not-symbol/slash, then just connect them like any other conditional statements.

Good luck!

[avengingangel]

When I took this prep test, I originally guessed on this question. But when re-visiting it un-timed, I came find the correct answer using the approach described in the explanation. However, fully diagramming each piece and converting to contraceptives can take up significant time, is there a way you can recommend to find the answer a quicker way? Something to recognize in the stimulus?

Also, what is the role of the first sentence/premise in the stimulus? It seems like its just there to distract you when trying to find the answer to the question. Thanks!

[Adam Tyson]

Good question, Angel. With regard to finding a shortcut for conditional reasoning, speaking for myself (and for a few of my colleagues that I have spoken with previously about this) the answer is no, there is no faster, easier way.

When I see conditional reasoning, if I see only two terms (if A, then B) I deal with it in my head. That's simple enough that I am not worried about getting things mixed up, and I can recognize the contrapositive when I see it. As soon as a third term (if a, then B and C, or perhaps if A, then B and if B then C, etc), I put pencil to paper and write it out. It may take an extra few seconds to do so, but it virtually guarantees that I will select the correct answer as easily as playing connect-the-dots. That also means that I will go through the answer choices faster and with greater confidence, typically saving me time overall on the question as compared to trying to keep it all straight in my head.

I've spoken to several fellow PowerScore instructors about this, and I have gotten almost complete agreement on it. These are all folks who have scored in the 99th percentile, so their advice is not to be taken lightly. I like to say "think with your pencil". You wouldn't try doing a conditional logic game in your head, so why do it on logical reasoning?

As to the first sentence, I wouldn't say it's there to distract you. It provides some important background information, framing the facts around which the argument is made. It's not a part of the conditional chain, so we don't need to analyze it, but it's nice to know what we're talking about.

[avengingangel]

Ok, thanks!