#10 - A ring of gas emitting X-rays flickering 450 times per

[Administrator]

Complete Question Explanation

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

Based on the facts in the stimulus, the ring of gas is in a stable orbit around a black hole. Also, the best explanation for the rate of flickering is that the ring has a radius of 49 kilometers. The last sentence, a conditional statement, is the key fact in this stimulus. Using the Unless Equation, we can translate that sentence as follows:

• Gas ring maintain orbit Black hole spinning

The rest of the stimulus suggests that the sufficient condition in this conditional statement has been met, since the gas ring is maintaining a stable orbit around the black hole at 49 kilometers. This means the necessary condition must also follow, and so the black hole must be spinning.

Answer Choice (A): While the stimulus gives us specific facts about gas rings that have radii of 49 kilometers or less, we do not know anything about gas rings that have radii greater than 49 km.

Answer Choice (B): The stimulus does not tell us anything about what kind of black holes emit flickering X-rays. This answer suggests that only stable orbiting rings of gas can emit flickering X-rays. The one black hole observed in the stimulus establishes that at least one stable orbiting ring of gas emits flickering X-rays. But that does not mean that these rings of gas are the only rings of gas that emit flickering X-rays. This answer choice is a good example of an Exaggerated Answer.

Answer Choice (C): This is the correct answer choice. Since the black hole in the stimulus is stable with a radius of 49 km, then according to the last sentence in the stimulus the black hole must be spinning.

Answer Choice (D): There is no information in this stimulus about what causes black holes to spin. This answer choice is another example of an Exaggerated Answer.

Answer Choice (E): This answer suggests that stationary black holes need gas rings with a radius of more than 49 kilometers. The contrapositive of the final sentence in this stimulus would suggest that if a black hole was not spinning, then it cannot be orbited by a gas ring with a radius of 49 km or less. Be careful with the logical opposites here. The fact that a black hole cannot be orbited by a ring of gas with a radius of 49 km or less does not mean that the black hole must be orbited by a ring with a radius greater than 49 km. It is possible that the black hole may not be orbited by any gas ring at all. Therefore, a stationary black hole does not require a gas ring of more than 49 km, and so this answer choice does not have to be true.

[lathlee]

Admin edit: due to LSAC policies and copyright law, complete LSAT questions cannot be posted online. However, posting in this section of the forum (Test Explanations) immediately identifies the question, and eliminates the need for the text to be posted. Note: you can quote small sections of the question as needed for your question.

This is how I broke down, rearranged down premises and conclusions, conditional equation, and used unless equation to make the argument make sense. I know question stem is must be true :

ALSO: plz criticize if my rephrasing techniques had any flaws.

Premise 1: a ring of gas emitting X-rays flickering 450 times per second has been observed in a stable orbit around a black hole.
Pr2: if the ring of gas has radius 49 kilometers, that rate of flickering can be best explained according to certain widely accepted physical theories.
Con: the gas ring could maintain an orbit so close to a black hole if only black hole was spinning.

The correct answer, according to the question providers, is C) but I don't understand why C is the correct answer. the information combined in question and question Stem, according to FACT TEST TM, there is no way to verify C must be true. I understand C) might be true since it is talking about the circumstances that isn't mentioned but might be true is type of common trap type of incorrect answer according to LSAT logical Reasoning book. Where in answer obtaining process that I got wrong?

NOW, I just realized that I used the unless equation incorrectly now I see why C can be correct answer. however, I still have a problem with this: i know people can observe the ring of gas if the ring of gas has radius 49 kilometers, that rate of flickering can be best explained....BUT RING of GAS that has radius of 49 kilmoeters = the black hole that is within the Ring of GAS (which is stated by C) ) ???? Isn't that false equivalency ?

[David Boyle]

Admin edit: due to LSAC policies and copyright law, complete LSAT questions cannot be posted online. However, posting in this section of the forum (Test Explanations) immediately identifies the question, and eliminates the need for the text to be posted. Note: you can quote small sections of the question as needed for your question.

This is how I broke down, rearranged down premises and conclusions, conditional equation, and used unless equation to make the argument make sense. I know question stem is must be true :

ALSO: plz criticize if my rephrasing techniques had any flaws.

Premise 1: a ring of gas emitting X-rays flickering 450 times per second has been observed in a stable orbit around a black hole.
Pr2: if the ring of gas has radius 49 kilometers, that rate of flickering can be best explained according to certain widely accepted physical theories.
Con: the gas ring could maintain an orbit so close to a black hole if only black hole was spinning.

The correct answer, according to the question providers, is C) but I don't understand why C is the correct answer. the information combined in question and question Stem, according to FACT TEST TM, there is no way to verify C must be true. I understand C) might be true since it is talking about the circumstances that isn't mentioned but might be true is type of common trap type of incorrect answer according to LSAT logical Reasoning book. Where in answer obtaining process that I got wrong?

NOW, I just realized that I used the unless equation incorrectly now I see why C can be correct answer. however, I still have a problem with this: i know people can observe the ring of gas if the ring of gas has radius 49 kilometers, that rate of flickering can be best explained....BUT RING of GAS that has radius of 49 kilmoeters = the black hole that is within the Ring of GAS (which is stated by C) ) ???? Isn't that false equivalency ?

Hello lathlee,

"the gas ring could maintain an orbit so close to a black hole if only black hole was spinning" is what you say above, but I think you mean "only if", not "if only". "If only" may be a sufficient indicator, and "only if" a necessary indicator.
And, the stimulus says the ring of gas is orbiting around the black hole, so that the hole is within the ring, and there's no false equivalency here.

Hope this helps,
David

[lathlee]

Thank you so much I learned a lot. I admit; i made mistake of if only part, you are right: I meant to say Only if.

But your answer kinda scared me a bit in a sense: I thought if only is necessary condition indicator but now you say it MAY BE sufficient condition indicator. So IF ONLY is more of sufficient conditioner indicator than Necessary condition indicator? How Can i distinguish which is which when IF ONLY is used in LSAT ? Thank you for the considerations,

Regards,

[Nikki Siclunov]

Hi lathlee,

"If only" is not an indicator of conditional reasoning. We use it to express a strong wish that things could be different. It means the same as "I wish," but is stronger. On the LSAT, the indicator we expect to see is "only if," which is a necessary condition indicator.

Hope this helps!

Thanks,

[jmramon]

I got this question right, but now this thread makes me feel like I misunderstood the stimulus and I’m not sure why. I would love clarification. Why are you guys saying the only conditional statement is the last sentence in the stimulus? What about the 3rd sentence? It says IF (a sufficient condition indicator) the radius is 49 km, then they can best explain the rate of flickering. I found this sentence, however to be largely irrelevant to getting to C when you all seem to say it’s integral to getting the answer. The first sentence of the stimulus about the observation of the ring of gas orbiting the black hole, in my opinion, fulfills the sufficient condition of the conditional conclusion, allowing us to conclude C (the necessary condition of the conclusion, that the black hole is spinning).

[Claire Horan]

Hi jmramon,

Although Powerscore identifies various words as indicating sufficient or necessary conditions, that doesn't mean that every time you see those words you should automatically diagram a SN relationship. You should try to decode the meaning of the sentence and make sure you understand the relationships.

In this example, we are told that a certain rate of flickering was observed. The stimulus goes on:

"In light of certain widely accepted physical theories, that rate of flickering can best be explained if the ring of gas has a radius of 49 kilometers."

What this sentence means is that, if the widely accepted physical theories, the ring has a radius of 49 kilometers.

The question stem asked us to assume the theories are correct, meaning we can assume the 49-km radius is accurate. This is not irrelevant to getting the right answer because, if we had not trusted the theories, we wouldn't be able to trust that the orbit is "so close" to the black hole and, thus, that the black hole must be spinning.