#18 - Each year, an official estimate of the stock of cod in

[elewis10]

Could someone please help me understand why C is incorrect. thanks so much.

[Shannon Parker]

Hey there,

Answer Choice C is incorrect because there is no information given in the stimulus by which to draw that inference. The stimulus does not give any information on the accuracy of the two different methods. Since this is a must be true question we are looking for an inference that can be drawn from the information given in the stimulus.

Since the estimate is taken by averaging the two different measurements, and one has gone up over the last ten years by roughly the same amount that the other measurement went up, we know that the most recent estimate should be fairly close to the one that was taken ten years ago because the change in the two measurements will average each other out.

Hope this helps.
Shannon

[oli_oops]

Hi Powerscore,

I can't really seem to agree your explanations of why A is correct, because to me, "the two estimates usually agreed closely" means what ever numbers they each were, they were the same/similar. For example, that can be research vessels = 9, commercial = 10. OR, research vessels = 5, commercial = 4. It's all RELATIVE. So "agreeing closely" every year doesn't necessarily mean the ABSOLUTE official estimate would be the same, if compared year to year.

Thus, now and 10 years ago might have a completely different ABSOLUTE value of official estimate.

Does anyone understand what I'm trying to say?

-Oli

[James Finch]

Hi Oli,

The key to understanding this question is the last clause of the final sentence in the stimulus. If the two estimates are moving in opposite directions but at the same rate, and are thus directly inversely proportional, then the average of the two (meaning adding both together and dividing the sum total by 2) would have to be roughly the same. As an example:

Sample A 10 years ago = 100 cod
Sample B 10 years ago = 100 cod
Average 10 years ago = 100 cod

Sample A this year = 200 cod (2x 10 years ago)
Sample B this year = 50 cod (1/2 10 years ago)
Average this year = 100 cod (same as 10 years ago)

Hope this clears things up!

[jerry]

I got this question right the second time when I reviewed it, but only after picking E my first time. However, I agree with Oli that the "by about the same amount" in the stimulus was tricky.

Like, in year 1 the average could be 100, with commercial and research both at 100.

But then in year 2, it could be:
commercial2 = 110 (+10)
research2 = 92 (-8)
average = 101

And in year 3, it could be:
commercial3 = 120 (+10)
research3 = 85 (-7)
average = 103

So by year 10, you could have:
commercial10 = 200
research10 = 30
average = 115

So even though the language in A is qualified, I think it's hard to determine if a change of 15% isn't "much different" from the estimate ten years ago. Like, if this were graphed, the upward linear slope of the commercial vessels could still be more extreme than the downward slope of the research vessels.

Still, that being said, I always knew that E didn't entirely make sense as an answer. I don't even remember why I chose that answer. I think it may have been because I thought if research vessels' average was markedly declining over the past ten years, then that would make it pretty improbable that the research vessel estimate could be anywhere smaller 20 years ago than where it is right now. And then, since we know that gap between research and commercial vessels' estimate didn't start to diverge until 10 years ago, then the average of commercial vessels and research vessels would both be the same — which would be a larger number.

But thinking about it once more, the research vessel's estimates over the years could look like a parabola instead of a straight line, or have multiple, drastic peaks and troughs for each year up until the past decade. We're only told that starting 10 years ago did a consistent trend start to occur for research vessels. So even though I still don't think it's probable that the amount of fish was lower 20 years ago, it's still, I guess, possible.

Overall, I didn't really think any of the answer choices was satisfactory. But that why it's a "most strongly supported" question.

[Brook Miscoski]

jerry,

I think that plugging in a ton of numbers is overthinking this question. The stimulus tells you that you get the official estimate by averaging two numbers. It then tells you that for 10 years, the sample number has been going down by the roughly same amount as the commercial number goes up. Mathematically, that means that the average is the roughly same, which is answer choice (A).

You can plug in some numbers to illustrate, but you have to be careful. The main problem with what you did is that you started off with a very small starting point and then by choosing a 20% difference between the increase and decrease and then maintained a similar huge difference between the increase and decrease. So of course you were going to get an answer that showed a serious move away from the original average, because you didn't follow the stimulus's rules (increase and decrease are about the same).

What made it hard for you to follow the stimulus rules is that you chose starting numbers that were way too small. Choosing larger numbers would also help you avoid unnecessary math. Imagine you chose 1,000,000 fish, because after all, it's fish, so we should chose a number that is higher in magnitude. Now it's easier to choose integer numbers that are close to each other, and the differences won't mean as much because of using an order of magnitude that has a common knowledge relationship to the topic.


Other choices:

(B) Stimulus says nothing about the number of vessels.
(C) Stimulus says nothing about which is more accurate.
(D) Stimulus does not take an "ought" position, it's an "is" stimulus.
(E) The only increase or decrease info we have is from the last 10 years, not the last 20 years.

[LearntheLSAT]

Hi all,

I've read the previous answers and responses, and while they make sense, I'm still trying to clarify (in simplest terms) why B is not correct. Could I simply claim that the because the stimulus creates an unequal comparison (the exact # of cod caught by research vessels compared to the average of number of tons of cod caught by various commercial vessels)? It's comparing an average to exact numbers, thus to create an official sample (another overarching average). Would this logic qualify and help eliminate the answer as well? Also, would this type of thinking work on similar questions? Thank you!

[Jeremy Press]

Hi LearntheLSAT,

Though I don't think the potentially unequal comparison you're referring to in the stimulus is the primary issue that makes answer choice B wrong here (in fact, you don't need to refer to the research vessels at all or the numbers of cod they catch to eliminate answer choice B), I do think you're on to the thing that's making answer choice B wrong: that the commercial estimate is based on an average tonnage calculated independent of the number of commercial vessels in the water. So, a rise in the commercial tonnage estimate doesn't necessarily tell you anything about the number of commercial vessels in the water. Rather, it simply tells you that more tons of cod are being caught for every kilometer of net set in the water for one hour. Since the average is not arrived at using the number of vessels, changes in the average won't tell you about changes in the number of vessels. The takeaway for future questions is that a change in an average doesn't tell you about changes in variables that are not part of the calculation of that average.

I hope this helps!

Jeremy

[ericsilvagomez]

Hi,

I read the initial explanation and the one immediately after it below, but there is still some confusion. Your explanation of how the numbers have changed over the years is good. However, I did not choose A because the second to last sentence says, "In previous decades, the two estimates usually agreed closely." And A states that last year's official estimate is not that different from the one ten years ago. But that is from the past decade, not the past decades, where the last sentence says there has been an increase for X and a decrease for why. I chose B after reading the first part of the last sentence, "however, for the last decade, the estimate based on commercial tonnage has been increasing markedly." Any help in identifying the flaw in my reasoning would be appreciated!

[srusty]

Hi,

I read the initial explanation and the one immediately after it below, but there is still some confusion. Your explanation of how the numbers have changed over the years is good. However, I did not choose A because the second to last sentence says, "In previous decades, the two estimates usually agreed closely." And A states that last year's official estimate is not that different from the one ten years ago. But that is from the past decade, not the past decades, where the last sentence says there has been an increase for X and a decrease for why. I chose B after reading the first part of the last sentence, "however, for the last decade, the estimate based on commercial tonnage has been increasing markedly." Any help in identifying the flaw in my reasoning would be appreciated!

Hi Eric,

I understand - this is a tricky one! The stimulus tells us that they get the official estimate by averaging the research vessel estimate and the commercial vessel estimate. It then goes on to tell us that the commercial vessel estimate has been higher than the research vessel estimate for the past decade, even though it used to be very similar to the research vessel estimate in previous decades. But, and most importantly to pick the answer choice, it tells us that the commercial estimate has been increasing by the same amount that the research vessel estimate has been decreasing.

Essentially, what this last clause is telling us is that the effect of the increase is offset by a decrease - so the overall average has stayed the same in the last decade. Answer choice (A) is best supported by this information.

Hope this helps!