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PT20.S1.Q24 - each december 31 in country q
skrishnan
Alum Member
Writing down my reasoning to understand better where I'm going wrong.
Available coal supplies = Total coal mined- Total coal consumed in a year
1991- Total coal mined =100
Total coal consumed= 70
Available coal supplies = 30
1990 - Total coal mined = 100
Total coal consumed = 50
Available coal supplies = 50
There are two possibilities I see-
1.Either there is less consumption in 90
2. More coal was mined in 90
This made me chose AC (D) . I feel like I'm missing something basic with answer choice B or my understanding of the stimulus is wrong. Any clarifications would be great!
https://7sage.com/lsat_explanations/lsat-20-section-1-question-24/
Comments
I think (but am not sure) that your formulation leads you astray in that both years are starting with 100. Not that your example is not helpful to sorting out the right answer, but it is only a piece of the puzzle.
Let's stick with your numbers for Available Coal
1991: 30
1990: 50
These numbers alone do support that D could be correct, but not that it must be correct. The trick to this question (and other similar questions involving numbers) is that you have to account for every variable. What your construction is labeling as Available Coal Supply is actually something more like Annual Net Coal Production. So the available coal supply in 1991 for you would actually be 80 as the 50 from the previous year would carry over. I'd take a second to look over the question with this new information and see if it makes sense. I'm also going to give you my in-question thought process to look at after reviewing.
The best strategy I've found for speed and accuracy on number questions is to think in extremes for each variable (if there is not an immediately correct answer to prephrase). Here is my thinking that I had going into the answers to rule out all of the incorrect choices quickly.
1) The three important variables are
How much coal was produced in a year
How much coal was consumed in a year
What is the total available
2) The total available must include the leftover coal from the previous year
3) 1991 had less Available Coal than 1990, but (key step in solution is right here) this result could come about either from using way too much coal in 1991 or from having very low production of coal in 1991.
(My extreme examples I ran quickly: What if 1991 literally produced no coal? What if 1991 used 10x's as much coal as 1990? This very quick thought experiment let me determine they were independent contributors. The reason I think extremes like this are helpful is because I can train them to be knee jerk reactions for these questions and do undetailed math to find the point very quickly.)
4) If both production and consumption can affect the answer independently, that means I can rule out any answer that says consumption or production was different than any other year. This is because even if production was 1, consumption could have been 0 and left me with more. If production was 10x's 1990, consumption could have been 100x's.
5) Prephrase: If I can't compare between years, I just need to make sure that I didn't produce more than I consumed.
5) Rule out Answer Choices
A: Compares production between years Out
B: Compares within one year Good and matches Prephrase Probably Correct
(I just put a tilde next to B in real time. I had a strong hunch it was correct, but new elimination was going to be easy so decided to rely on that)
C: Compares consumption between years Out
D : Compares consumption between years Out
E: Compares between one half and the other - this is irrelevant as we are only thinking in terms of years. Out
Hey there!
Nowhere in the question does the author/narrator mention the amount of coal mined or consumed. All you know is that coal leftover in 1990 > coal leftover in 1991. Now, coal leftover in 1990 carries over in 1991. All we know is that the amount we have in 1991 is lesser than the amount in 1990. What does this mean? Certainly, whilst inheriting the coal from 1990, coal was mined in 1991 too. But, if we have a lesser amount in 1991, that MUST mean that the coal we consumed in 1991 was more than the coal we mined in 1991.
You're assuming that the amount of coal mined in each of the two years is the same. Moreover, you're assuming that the coal leftover in 1990 doesn't carry over to 1991. So your entire reasoning is based on hypotheticals which only may be true.
AC (D) may be right, but isn't necessarily right. It's entirely possible for them to enter in a net deficit in 1991 by consuming lesser coal than 1990, but consuming more than what was mined in 1991. For instance:
1990
(mined) 100 - (consumed) 50 = 50
1991
(leftover from last year) = 50
(mined)20- (consumed)40 = -20
total left over coal on Dec 31st = 30
You see how this refutes AC (D)?
@thisissparta Thanks for the explanation, I am still slightly unsure of this part of your explanation " Certainly, whilst inheriting the coal from 1990, coal was mined in 1991 too. But, if we have a lesser amount in 1991, that MUST mean that the coal we consumed in 1991 was more than the coal we mined in 1991."
How can we be so sure of this? Since we have a lesser amount of total leftover coal? Couldn't it be the amount left over was 10, coal mined was 60 and the coal consumed was 30. This would leave us with total left over coal as 40, which could still be less compared to 1990?
If the coal leftover was 10 from 1990, then the coal leftover in 1991 (40, as per your example) would be greater than the coal leftover in 1990. That would be the antithesis of the passage. The passage says left over coal in 1991 < 1990.
Let me break it down for you further. Let X = coal leftover in 1990 and carry forwarded in 1991; let Y = coal mined in 1991; let Z = coal consumed in 1991.
In order for the sum of X + Y - Z to be equal to a number < X, Z has to be a number greater than Y.
@thisissparta Thank you so much for this! I needed a break. Came back to it and it was completely clear. Sorry about the dumb question
No worries! Sometimes one gets so engrossed in trying to parse dense passages that it's easy to lose sight of the primary elements of the passage -- happens to everyone so it's totally understandable!
I'm glad that you got it! It wasn't an easy question, for sure.
but why? Why would you assume that? Suppose that the remaining coal from 1990 was put in storage (or destroyed at the end of the year) and the data used for 1991 was from coal freshly mined in that year only? Why are you assuming that coal from the previous year HAS to be carried over?
I think that is one of my issues with this question. Too many assumptions being made that aren't commonplace.
Grateful for your response ( or anyone else's)
If we don't know anything about what was mined or consumed, how are you so sure that what was leftover in 1990 was carried over to 1991?
we are given one fact: amount in 1991 was considerable lower than in 1990. From that statement, where do you get that the leftover amount in 1990 was carried over to 1991? The two numbers itself are being compared. How does that infer that the amount leftover 1991 was from what was "inherited" from 1990?
Please help!
OK, this explanation helped.
Year's 1991 and 1990 are not entirely independent.
We know from the question that there was, in fact, coal leftover in 1990 - the premise states that the coal leftover in 1990 was greater than the coal leftover in 1991. So, keep this in mind: there is coal leftover in 1990. What happens to that coal? I think it can presumed, with a great degree of certitude, that any leftover supplies will become a part of the total stock of coal for the year 1991. If we have leftover coal on December 31st, 1990 at 11:59 PM, that would be a part of the stock of coal on January 1st, 1991, 12:00 AM.
Now, if we were to calculate the total coal the country had throughout the year on December 31st, 1991, it would be the summation of the inherited stock from 1990 and the coal produced in 1991.
@tams2018 All good questions! There's a lot to unpack in this one. We know the coal gets rolled into the supply, in addition to what @thisissparta said because we know we are considering "the total amount of coal that has been mined throughout the country but not consumed," as well as "Country Q has not imported or exported coal since 1970." That last bit is probably the most important. It seems like extraneous information, but it is really a subtle way of telling us what you're asking about - the unused has nowhere to go so it must go into the "total available coal supply."
Hope that helps!