#17 - On average, city bus drivers who are using the new

[Administrator]

Complete Question Explanation

Parallel Flaw. The correct answer choice is (C).

Answer choice (A):

Answer choice (B):

Answer choice (C): This is the correct answer choice.

Answer choice (D):

Answer choice (E):

This explanation is still in progress. Please post any questions below!

[reop6780]

I got the question right.

I was just curious of expression such as "generally" and "on average."

When I was studying LR bible, there were some words that were meant to be "some," and "most."

For example, "usually," and "typically" are categorized under "most."

Is "generally" under "most"?

Also, is "generally" meant to imply situations being more frequently held than "on average"?

[Ron Gore]

That's a great question, Reop.

The word "generally" implies the group as a whole, though taking into consideration that there may be exceptions not covered by the sweeping description. So, in answer choice (E) to the question you reference, the second sentence could be understood: "as a whole, ignoring any exceptions, lawn mowers powered by electricity require less maintenance than do lawn mowers powered by gasoline." However, don't confuse this term with "all" which precludes the possibility of exception. You can think of it as "most." To cross-reference the conversation with our Logical Reasoning Bible, the list on page 308 of the January 2013 version includes the word "typically," which is synonymous with "generally."

The word "average," used in both the stimulus and the correct answer choice, (C), has a very different context than "generally," and expresses a specific numerical relationship among numbers. Because the average is, to quote Merriam-Webster, "a single value (as a mean, mode, or median) that summarizes or represents the general significance of a set of unequal values " you have to be cautious of conflating that result with the idea of "most."

In the stimulus to the question you referenced, there were bus drivers using the old system, and bus drivers using the old system. To simply discuss the difference between "most" and "average," consider this example.

You have five drivers using the old system and five drivers using the new system. On a scale of 1 to 10, with 10 being the best time record possible, let's say the results are:

Old: 5, 5, 5, 5, 5

New: 10, 9, 4, 4, 4

Although most of the drivers using the new system had a worse time record than any of the drivers under the old system, the average record of drivers under the new system was higher (6.2) than the average record of those under the old system (5).

Hope that helps sort out the meanings.

Ron

[reop6780]

Thank you so much for the details! It helped me a lot!

[ngreen221]

Hello PS,

I read through the stimulus and thought that the flaw was a simple Mistaken Reversal. My reasoning is as follows:

P: Use new fare collection system ---------> better on time record
C: M has best on time record --------> using computerized fare collection system

I attacked the answer choices based on this and immediately saw A as having a mistaken reversal as well:

P: Acquired after 1998 -----> large capacity
C: Vehicle has largest capacity ------> acquired after 1998

I answered A confidently and moved on, only to see that the correct answer is C. May I please have an explanation on my logic and the mistakes I made?

Really appreciate it!

[Brook Miscoski]

ngreen,

The reason that you can't simply look for a Mistaken Reversal is that the stimulus is not based on conditional reasoning. Instead, from our common errors of reasoning list, it is most like an error of composition.

The stimulus establishes the average characteristic is that drivers using the new computerized systems have better on-time records, but that does not mean that characteristic is found in each member of the group (after all, it's an average). That is why (C), and not (A), is correct.

If you did approach this as a Mistaken Reversal, you could still get it right by making sure the concept of "average" is preserved. Because (A) is absolute ("all"), it cannot reflect all of the logical elements of the stimulus. That's another reason to review all of the answer choices before moving along.

[madisonzill]

Can you explain why the other answers are wrong. I got the correct answer, but I want to make sure that my reasoning was correct.

[KelseyWoods]

Hi Madison!

There are multiple reasons to get rid of any of these answer choices so it might help if you told us your reasoning and then we could confirm whether your reasoning was sound or not.

Ultimately, they're all wrong because none of them match the flaw in the stimulus. But I would get rid of (B), (D), and (E) right away because their conclusions don't match the conclusion in the stimulus. The conclusion in the stimulus is very certain: "she must be using the computerized fare-collection system." But in (D) and (E), the conclusions contain a "probably": "Last week's snowstorm in Toronto was probably an average storm for the area" and "it will probably require a lot of maintenance." Degree of certainty is important when it comes to matching conclusions in Parallel Reasoning questions. If I have a certain conclusion in my stimulus, I don't want a conclusion in my answer choice that is qualified with "probably." Similarly, answer choice (B) says "he is undoubtedly taller than most of the members of the gold team." The word "undoubtedly" is definitely certain, but "taller than most" is not really the same as "she must be using the system." Instead, it's a comparative conclusion--it's comparing Henri to the members of the other team and saying he's taller in comparison to most of them. The stimulus conclusion is not a comparative conclusion, so I don't want a comparative conclusion in my correct answer.

In answer choice (A), the conclusion matches, but the one of the premises does not. The premise in the stimulus is an on average comparison between drivers using the system and drivers not using the system. The premise in answer choice (A) is a conditional statement giving a characteristic of all solid-waste collection vehicles acquired after 1988 and has no concept of "average." Thus, I can eliminate answer choice (A) and I'm left with (C).

Again, you could have approached this question differently and there are other reasons for eliminating those answer choices. So feel free to elaborate on your thinking and we can let you know if you reasoning was correct!

Hope this helps!

Best,
Kelsey

[gingerale]

I'm confused about an earlier post on this thread by PS staff that the error in this stimulus is not conditional but an error of composition. I immediately noticed what I thought was a mistaken reversal in the conclusion of the stimulus and started looking for that in the answer choices. This helped me narrow my choices down to (A) and (C), but I ended up choosing (A). I see how recognizing the error of composition could have helped me choose the correct answer, but I'm still struggling to see this flaw in the stimulus. What is the error of composition in this stimulus and how can I work on noticing it in future stimuli?

[Robert Carroll]

gingerale,

This is not the error of Composition (Part to Whole) but the related error of Division (Whole to Part). On the average, and thus overall, there is a correlation between the new fare-collection system and the on-time record. That doesn't mean that any individual will exemplify that correlation well - it's possible for an outlier to have the new system but be bad at being on time, and vice versa. So the general quality of the whole collection of drivers is imputed to an individual driver. That's an error in answer choice (C) but not answer choice (A).

Robert Carroll