#24 - Each December 31 in Country Q, a tally is made of the

[menkenj]

I found this question to be helpful to write out the math of the stimulus.

(M1990 - C 1990 + M1991 - C1991 ) < (M1990-C1990)

The performing basic math. The M1990 and -C1990 are on both sides so those cancel out.
We are left with:

M1991 - C1991 < 0
M1991 < C 1991


I have been working on understanding which #% problems are best solved with basic math and which are not.
I haven't worked out a full fledged system yet but for this problem it really was the best way to solve it IMO.
The intuition of the above explanations are great too but for me personally I found the concreteness of the math much faster and easier to see.

[fk98]

Hi A,

The first statement in this stimulus is what often gives people trouble. It's deceptively tricky. What it tells us is that Country Q makes a tally of the total available coal supplies at the end of each year. That tally is NOT the amount mined minus the amount consumed. It's basically just how much coal they have on hand.

Let me give you an analogy. As an LSAT instructor, I carry a lot of pencils and I tend to lose them or give them away so I often need to buy more. Let's say I tally my pencil stock at the end of each year. At the end of 2012, I had 10 pencils. At the end of 2013, I had 4 pencils. Based on these facts, you really don't know anything about the specific amount of pencils I bought or lost in either year. All you know is that at the end of 2013, I had fewer pencils than I had in 2012. Maybe I didn't buy any pencils in 2013 but I lost 6 and that's why I'm only left with 4. Or maybe I bought 500 pencils in 2013 and I lost 506 of them and that's why I'm only left with 4. You have no idea. But what you do know is that I lost more than I bought in 2013 because I ended up with fewer pencils by the end of the year than I had at the start.

That same concept holds true here. We don't know specifically how much coal Country Q mined or consumed in 1991. We can't make any comparisons between 1991 and 1990 in terms of how much coal was mined and consumed in each year (which is what both answer choice (A) and (D) do). But we can say that if Country Q has less coal at the end of 1991 than it had at the start of 1991, they must have consumed more coal than they mined.

The "tally" concept is really what makes this a tricky concept. But once you figure out what that means, it isn't so bad

Hope this helps!

Best,
Kelsey

Hi Kelsey, this explanation makes so much sense thanks! So to clarify, if the value for 1990 was 10, then 1991 would start with 10, and then it doesn't matter if Q mined more or not that year because the value would still be less than what it was at the beginning, and thus in 1991 more was consumed than mined. Is this correct?

[Jeremy Press]

Hi fk,

Yes, you've got it! If they start 1991 with 10, and end 1991 with 9 or less, then there's no way the country mined more than it consumed during 1991 (because if they had, they'd end 1991 with 11 or more). Keep up the good work!