PT7.S4.Q13 - The National Assoc. of Fire Fighters says

Markmark

help This question gave me trouble but I think I understand now. Here's my explanation, please let me know if it's right.

Conclusion: early detection of fire is no more likely now than it was 10 years ago
Premise1: 10 years ago 30% of houses had detectors, now 45% do
Premise2: but over half detectors are either inoperable or don't have batteries.

I chose A which says "15% of detectors were installed over the last 10 years." This isn't a trigger for the conclusion, and it doesn't connect the dots, because this premise just doesn't lead the premises any closer to the conclusion. If we said "All detectors installed in the last 10 years, which accounts for 15% total, are all defected or inoperable" this would guarantee the conclusion. This would allow us to say that indeed even though there are more detectors total, early detection is still equally likely as it was 10 years ago.

D makes sense now but I eliminated it because it doesn't need to be that the detectors are inoperable (which is 1 explanation of the 2), they could just have no batteries (the 2nd of the 2 explanations). I thought "D doesn't need to be true, there could be an alternate explanation." However, this explanation, despite the existence of other explanations, does connect the dots between the premises and the conclusion. Now we could say we have more detectors overall, but the proportion of inoperable detectors increased a lot so now the early detection rate is the exact same.

A parallel argument would be "We installed 15% more security cameras than a year ago but vandalism rates are the same. This is because the proportion of working security cameras dropped over the last year. As a result, roughly the same amount of security cameras were of use, and we weren't able to prevent more vandalism despite having more cameras."

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BlindReviewer

"I thought "D doesn't need to be true, there could be an alternate explanation." However, this explanation, despite the existence of other explanations, does connect the dots between the premises and the conclusion. Now we could say we have more detectors overall, but the proportion of inoperable detectors increased a lot so now the early detection rate is the exact same."

I think you're exactly right here -- this is a sufficient assumption question where all you're trying to do is build the bridge (whether it's an exact fit to the conclusion or more than enough to make it true) to the claim. Sure there can be many other ways to make the conclusion work, and you give a good one in your explanation (all of the newly installed ones don't work) but we just need one of them as an answer choice.

Markmark

@BlindReviewer said:
"I thought "D doesn't need to be true, there could be an alternate explanation." However, this explanation, despite the existence of other explanations, does connect the dots between the premises and the conclusion. Now we could say we have more detectors overall, but the proportion of inoperable detectors increased a lot so now the early detection rate is the exact same."

I think you're exactly right here -- this is a sufficient assumption question where all you're trying to do is build the bridge (whether it's an exact fit to the conclusion or more than enough to make it true) to the claim. Sure there can be many other ways to make the conclusion work, and you give a good one in your explanation (all of the newly installed ones don't work) but we just need one of them as an answer choice.

Right, this isn't a steel-built suspension bridge bazooka that's blasting the argument into guaranteeing the conclusion, it's more of a weird rope bridge that I'm thinking "Huh I guess that works..."