Q13 - The National Association of Fire

[b91302310]

I could not understand why (C) is correct. Could any one provide the full solution for this ?

Thanks

[aileenann]

Sure thing! Here is my full solution from top to bottom.

First thing is to check out what the question type is. This question is an assumption question. Moreover, they are asking specifically for a necessary assumption.

Now let's formulate the core of the argument. I think it goes like this:

The percent of homes with fire alarms has increased but over half are without batteries or not functional -> (therefore) The detection of fires has not become any more likely.

But what seems to be missing? I always ask myself this before even glancing at the answer choices. Here, I have a sense I'm looking for something about what percentage of the fire alarms were working in the past - after all, it might even have been a low percentage of functioning fire alarms years earlier! But then again, there might be other assumptions I am missing but that are correct.

(A) is completely out of scope - I don't care when they were installed, I care how likely it is that a fire will be detected in time.

(B) is wacky and hard to think about - would where the fires are happening (i.e. in what kind of house) make a difference to the likelihood of detection? This is the sort of hard to think about answer I am going to avoid unless I cannot find anything else that looks likely.

(C) doesn't seem to matter. It just provides an alternate reason why some of the smoke alarms don't have batteries - but that's not enough to make the conclusion either right or wrong, it's too squishy. This doesn't tell us anything and is not the answer.

(D) looks pretty good - in fact looks quite a lot like what I was looking for. After all, if the percentage of broken fire alarms is going up, then it matters less or not at all from a safety perspective that there are more fire alarms than there used to be. This supports the conclusion and is our answer.

(E) is out of scope - we don't care about how fire detectors compare to other safety mechanisms.

So (D) is our answer. Please let me know if you have any questions or comments on this one!

[b91302310]

Oh! I misread the correct answer (D) with (C). However, the explanation helps a lot. I still have few questions concerning this one.

1. Does the "early" detection mean the detection in earlier years or the detection in the early stage of a fire?

2. After getting a better understanding of this question, I think it is easier for me to regard this question as a question type of solving the paradox. The paradox will be why the percentage of homes having smoke detectors has increased over the past ten years whereas detection of house fires is still no more likely. Thus, answer choice (D) provide the explanation that owing to the percetange of inoperative fire detectors also went up proportionately. Does that make sense?

Thanks again for the clear-up.

[aileenann]

(1) It means early stages of the fire - we can see this from context. It wouldn't be very interesting to think about the probability of detection in early years - that's just one static number.

(2) Yes, here I think that a necessary assumption is also a way to explain the paradox. That is, it's not a paradox once we assume certain things about the world.

Thanks for the follow-up!

[perng.yan]

i seem to still have problems with this question for some odd reason....

premise:
fire alarms in homes has increased.. yet... over half of them are w/out battery or inoperative

conclusion:
detection is still not more likely


i don't see why the author has to assume that proportion of inoperative detectors has increased...

thanks.

[perng.yan]

oh.. is it because we can argue that the smoke detectors ten years ago used to be even MORE inoperative? therefore.. although more than half are still inoperative... but it's still an improvement AND more homes now have detectors.. so early detection can still increase...

therefore.. making (D) says.. well.. ASSUMING that inoperation has increased..

i'm not sure if my reasoning is sound...

[ManhattanPrepLSAT1]

oh.. is it because we can argue that the smoke detectors ten years ago used to be even MORE inoperative?

Not exactly. Answer choice (D) says that smoke detectors ten years ago used to be even more operative. It must be true that the smoke detectors have become less operative. If they had not, then since more homes have smoke detectors, the likelihood of early detection of fire would increase.

The conclusion of this argument is that early detection has not increased. An assumption of the argument is that detectors are less operative now - which is what answer choice (D) is suggesting.

Does that help clear this up?

[perng.yan]

yea.. it makes sense when i step away from the problem and see that it's totally logical. thanks.

[peg_city]

I will give a numerical example....I hope it's right

45% - now
30% - 10 years ago
Conclusion - 'No more likely'


50% of 45% now = 22.5%

50% of 30% 10 years ago = 15%

22.5 > 15 therefore (D)

[mfowler]

I will give a numerical example....I hope it's right

45% - now
30% - 10 years ago
Conclusion - 'No more likely'


50% of 45% now = 22.5%

50% of 30% 10 years ago = 15%

22.5 > 15 therefore (D)

I would beg to differ. I'll use your example:

50% of 45% now = 22.5%
50% of 30% earlier = 15%

Your conclusion is not supported by answer choice (D). Your example shows that the proportion of inoperable fire detectors remains constant at 50%. Thus, these numbers (22.5 > 15) indicate that fire prevention has actually risen. After all, 22.5% fire prevention is better than 15%. This is not in line with the stimulus, which claims that early detection is "no more likely."

Instead, consider this:

50% of 45% now = 22.5 % (this is the likelihood of fire prevention - we can assume that since 50% are inoperable, the other 50% are not inoperable - or operable)
25% of 30% earlier = 7.5% (this is the amount inoperable smoke detectors, which we'll have to subtract from the 30% to get the number of operable smoke detectors) = 30% - 7.5% = 22.5% (this is the likelihood of fire prevention).

In this second scenario, you clearly notice that fire prevention between the two years is the same. This satisfies the stimulus which reads, "early detection of fires [are] no more likely". For this to be the case, however, the proportion (in red) of inoperable smoke detectors must have risen, as shown here. Hence, answer choice (D).

I'm quite new to the LSAT, and even though I got this answer right after a couple of minutes, I have a hard time understanding how I might be able to answer it in the average of 1:25 minutes allotted (on average) to each question.

[sonssi13]

hi guys

thanks to the previous explanations above, I totally understood why (D) is the right answer.

But I'm still confused with (B), which I chose as the answer, as to why it's the wrong answer choice.

Could someone illuminate the reason to eliminate (B)? thanks.

[WaltGrace1983]

hi guys

thanks to the previous explanations above, I totally understood why (D) is the right answer.

But I'm still confused with (B), which I chose as the answer, as to why it's the wrong answer choice.

Could someone illuminate the reason to eliminate (B)? thanks.

In short, (B) is wrong because the number of fires each year (a raw #) has nothing to do with the likelihood of preventing those fires (a %). We simply don't need to know anything about how many fires are occurring.

30% of homes had smoke detectors then
+
45% of homes have smoke detectors now
+
Half of smoke detectors now are inoperative
-->
Detecting house fires = no more likely

The gap is that we don't know about how many smoke detectors were inoperative then. What if all smoke detectors then were inoperative? The assumption will have to do with something regarding this issue. It will say something about the percentage of inoperative smoke detectors back then.

(A) A bit confused on why this is even here. Couldn't it be that 15% of the smoke detectors were installed exactly 10 years ago? Either way, this doesn't really attack the gap.

(B) Reasoning above.

(C) Even if all the smoke detectors were battery operated, so what?

(E) We don't need to know about water sprinklers.

I do have a question about (D) though. Does the percentage of smoke detectors that are inoperative have to INCREASE? Can't it stay the same and still be necessary? I guess that would get at the # vs. % problem though.

[Mab6q]

It is necessary for the proportion to increase, because if we negate D and it stayed the same, then that would weaken the argument. If 10% of detectors were inoperative 10 years ago and now 10% are inoperative now, that coupled with the increase in homes that have detectors would break the argument.

[kat_bustamante]

This is not a necessary assumption question guys. This is a sufficient assumption.

[ohthatpatrick]

No, it's a Necessary Assumption (with funky wording). There are only a handful of these in the LSAT canon.

You're probably thinking Sufficient Assumption because the question stem uses the phrasing "conclusion properly drawn", which is usually reserved for Sufficient Assumption.

But, the question stem says "In order for the conclusion to be properly drawn, which assumption would have to be made?"

That is definitely asking which assumption is NEEDED.

EXAMPLE:
The cake costs $20. Thus, Joe has enough cash to buy it.

In order for that conclusion to be properly drawn, which assumption must be made:
A) Joe has at least $3.
B) Joe has $50.


Which is the right answer?

(A). We have to assume he has at least $3, because if he had less than $3, the conclusion could not be properly drawn.

We don't HAVE to assume that Joe has $50, because even if he didn't have $50, the conclusion could still be properly drawn.

Here's another famous example of that weird question stem that looks Sufficient but is actually Necessary:
https://www.manhattanprep.com/lsat/foru ... t-t29.html

[jeanne'sjean]

So am I right that in this stimulus the NUMBER is not relevant since the PERCENTAGE can also sufficiently indicate a trend? In other words, even if the number of homes in the community declines a lot leading to less homes with smoke detectors even with a percentage of 45%, we can also conclude that the early detection of house fires is no more likely?