#13 - The National Association of Fire Fighters says that 45

[Rachael Wilkenfeld]

Hi y GGIBA003,

We are not crossing numbers and percentages here. We are only comparing percentages to each other, so we don't have an issue with not knowing the total number of a thing. We aren't trying to figure out how many smoke detectors there are, but we are trying to figure out information about percentages of houses that have them, or smoke detectors that are working/not working.

We can't really do the negation here without understanding the math behind it. You correctly negated the statement, but it doesn't have enough clear meaning to you without the math. So let's go through that again.

The author concludes here that people are no more safe today than they were in the past because over 50% of the smoke detectors are inoperable. Our negation then should make that conclusion less likely, that should say that we are safer today than in the past.

Our options for smoke detector working compared by years:

1. Same now as in the past. Now-50% + don't work. 10 years ago 50% don't work
We multiply the percentage of houses with smoke detectors with the percentage that work. Here, if 50% don't work, 50% do. We multiply 50% times the number of homes with smoke detectors (30 % in the past, 45% now).

Percentage of safe houses Now: (45%*50%=22.5%) 10 years ago (30%*50%=15%)

We are safer now because 22.5% is higher than 15%. This weakens the argument by showing that we actually ARE safer now.

2. More inoperable in the past than now. Now 50% don't work. Then 70% don't work.
We do the same process as above, 50% work in the present, 30% worked in the past.

Percentage of safe houses Now (45%*50%-22.5%) 10 years ago (30%*30%=9%)

We are safer now because 22.5% is higher than 9%. This also weakens the argument because we are safer now.

3. More inoperable now than in the past. Now 50% don't work. Then 20% didn't work.
That means that 50% do work now, and 80% did work in the past.

Percentage of safe houses now (45%*50%-22.5%) 10 years ago (80%*30%=24%)

We are no more safe now than we were then. This is consistent with the argument.


Our conclusion requires that the final situation be true, more inoperable now than in the past. That's the only situation where we see that more houses were safe before than now, as consistent with the conclusion. The negation of answer choice (D) is the first two examples, and shows that we ARE more safe now than in the past. That's inconsistent with the conclusion drawn in the passage.

I hope that helps! I know it can be tempting to avoid the math, but it's worth it to work through with numbers to make the concepts clear.

[jennifersuh]

Hi!
I have a question about the question stem here--how would I have known to differentiate this from a Justify question?

Thank you!

[Ryan Twomey]

Hey Jennifer,

This is an amazing question, and I'm glad you're paying attention to the stems in such a specific way. It is a good sign for your success on the exam.

So, I'd say 90 percent of the time when the word assumption is paired with the phrase, "allow the conclusion to be properly drawn" the question is going to be a justify the conclusion question. The only exception is when this combined phrasing is also paired with some type of necessary phrasing like "must" or "needed" or "have to" or "required". This necessary phrasing makes it an assumption question automatically. This will make the negation test important and necessary to perform since the question is asking what is required for the conclusion to be properly drawn instead of just asking which one of the following answer choices would allow the conclusion to be properly drawn.

I hope this helps. This is rare, so I would not get overly concerned, but it is still a great thing to know, especially if you want to be a very high scorer and know every possibility.

I wish you all of the luck in your studies and keep posting.

Best,
Ryan

[lsatstudying11]

Hello there,

Would another thing being assumed here be that the number of inoperative smoke detectors has not decreased? Because, if the number of inoperatives have decreased, then the jump from 30 to 45% would force it to be the case that early detection is more likely.

I thought about this because I am struggling a bit to really wrap my head around why this is a % issue and not a number issue. I can see how an answer saying that 'the number of inoperative smoke detectors has increased' would be bad because the change from 30 to 45% would account for this, but feel like it must be necessary that the number of inoperatives did not decrease. Is this an ok way of thinking about this? Thank you

[Rachael Wilkenfeld]

Hi lsatstudying,

Remember we aren't worried about absolute numbers here. We have no idea how many total houses there were in the past or present. You might think that the numbers of homes are probably similar. They might be, they might not be. It could be there was a huge housing boom over the past 10 years. Or, maybe there was a natural disaster that wiped out almost all of the housing stock. We are just worried about the percentage of houses with working or inoperable smoke detectors.

Here are the potential changes with sample percentages, and how they would impact the argument.

1. Same now as in the past. Now-50% + don't work. 10 years ago 50% don't work
We multiply the percentage of houses with smoke detectors with the percentage that work. Here, if 50% don't work, 50% do. We multiply 50% times the number of homes with smoke detectors (30 % in the past, 45% now).

Percentage of safe houses Now: (45%*50%=22.5%) 10 years ago (30%*50%=15%)

We are safer now because 22.5% is higher than 15%. This weakens the argument by showing that we actually ARE safer now.

2. More inoperable in the past than now. Now 50% don't work. Then 70% don't work.
We do the same process as above, 50% work in the present, 30% worked in the past.

Percentage of safe houses Now (45%*50%-22.5%) 10 years ago (30%*30%=9%)

We are safer now because 22.5% is higher than 9%. This also weakens the argument because we are safer now.

3. More inoperable now than in the past. Now 50% don't work. Then 20% didn't work.
That means that 50% do work now, and 80% did work in the past.

Percentage of safe houses now (45%*50%-22.5%) 10 years ago (80%*30%=24%)

We are no more safe now than we were then. This is consistent with the argument.

We don't have to know that the number didn't decrease, because we don't know the change in the number of houses (if any). We do have to know more than just the number didn't decrease---we have to know that the percentage of inoperable actually increases.

Hope that helps!