It should be B

Tough one. I will go for A

Each December 31 in Country Q, a tally is made of the country's total available coal supplies--that is the total amount of coal that has been mined throughout the country but not consumed. In 1991 that amount was considerably lower than it had been in 1990. Furthermore, Country Q has not imported or exported coal since 1970.

Important to note here: the amount the question refers to is not the amount of coal mined or consumed -- it is the DIFFERENCE between the amount of coal mined and the amount of coal consumed. That DIFFERENCE was greater in 1990 than in 1991, and we are only concerned with in-country info here -- no imports or exports. Also important to realize -- the total available coal supplies must include coal mined in previous years that has gone unconsumed.

If the statements above are true, which one of the following must also be true on the basis of them?

A) In Country Q, more coal was mined in 1990 than was mined in 1991.

This is possible, but we're looking for a must-be-true. It is equally possible that in 1990, Country Q mined 3 tons of coal and consumed 1 ton, but in 1991, Country Q mined 3 tons of coal and consumed all 3 tons. This would leave the 1990 and 1991 figures equal to one another. Eliminate.

B) In Country Q, the amount of coal consumed in 1991 was greater than the amount of coal mined in 1991.

This is the only one that MUST BE TRUE in order to satisfy the terms of the question. If (for example), Country Q mined 3 tons of coal in 1990, and consumed 1 ton, they would have 2 tons left over. For the number to be smaller in 1991, they would have to consume MORE than than they produce in order to cut into the 1990 figure.

C) In Country Q, the amount of coal consumed in 1990 was greater than the amount of coal consumed in 1991.

This is impossible. Eliminate.

D) In Country Q, the amount of coal consumed in 1991 was greater than the amount of coal consumed in 1990.

This is possible but again, doesn't NEED to be true. For example, if Country Q produced 3 tons of coal in 1990, consumed 2.5 tons and had a .5 ton difference, then in 1991, produced 1 ton of coal and consumed 1.2 tons, they would have a .3 ton difference and the terms of the question would still be satisfied. Eliminate.

E) In Country Q, more coal was consumed during the first half of 1991 than was consumed during the first half of 1990.

This is out of scope, since we are not concerned with "half years" here, only the full year. Eliminate.

I love these - they are like brain exercises. I have been reasonably sure about my answers in the past but I'm not sure about this one -- I'm interested to see the OA and reasoning.

D) In Country Q, the amount of coal consumed in 1991 was greater than the amount of coal consumed in 1990.

This is possible but again, doesn't NEED to be true. For example, if Country Q produced 3 tons of coal in 1990, consumed 2.5 tons and had a .5 ton difference, then in 1991, produced 1 ton of coal and consumed 1.2 tons, they would have a .3 ton difference and the terms of the question would still be satisfied. Eliminate.

Please pay attention to the phrase : Country Q has not imported or exported any coal.So I believe the production is constant. Only the consumption varies.

What do you say?

Whether they have imported or exported coal has little to do with production -- it doesn't imply that production is constant. For example, the US could produce 22 tons of corn in 2007 and 25 tons in 2008, disregarding any imports or exports. Country Q could end the year with a surplus of coal (though they couldn't end it with a shortage).


What indicates that production is constant?

To be honest none of the options MUST be true. But B has fewer variables compared to the rest so I would go with B.

myohmy wrote:Whether they have imported or exported coal has little to do with production -- it doesn't imply that production is constant. For example, the US could produce 22 tons of corn in 2007 and 25 tons in 2008, disregarding any imports or exports. Country Q could end the year with a surplus of coal (though they couldn't end it with a shortage).


What indicates that production is constant?

Agree with you. Production is not constant. But take a look at B.
It says coal consumed > coal mined

so,this means
coal consumed = 8 tons
coal mined = 6 tons

so, the amount left over (difference) is negative .

So, still B is correct?

B for me

gmat740 wrote:

myohmy wrote:Whether they have imported or exported coal has little to do with production -- it doesn't imply that production is constant. For example, the US could produce 22 tons of corn in 2007 and 25 tons in 2008, disregarding any imports or exports. Country Q could end the year with a surplus of coal (though they couldn't end it with a shortage).


What indicates that production is constant?

Agree with you. Production is not constant. But take a look at B.
It says coal consumed > coal mined

so,this means
coal consumed = 8 tons
coal mined = 6 tons

so, the amount left over (difference) is negative .

So, still B is correct?

You're forgetting that the total coal in existence in 1991 includes the unconsumed coal from 1990. If it didn't, if country Q imported no coal, obviously B would be impossible since you can't consume more than you have of something. If Country Q produced 6 tons in 1991, and consumed 8, then they HAD to have at least 2 left over from 1990 (this is our 1990 figure) meaning that the 1991 figure is 0, smaller than 2.

myohmy wrote:

gmat740 wrote:

myohmy wrote:Whether they have imported or exported coal has little to do with production -- it doesn't imply that production is constant. For example, the US could produce 22 tons of corn in 2007 and 25 tons in 2008, disregarding any imports or exports. Country Q could end the year with a surplus of coal (though they couldn't end it with a shortage).


What indicates that production is constant?

Agree with you. Production is not constant. But take a look at B.
It says coal consumed > coal mined

so,this means
coal consumed = 8 tons
coal mined = 6 tons

so, the amount left over (difference) is negative .

So, still B is correct?

You're forgetting that the total coal in existence in 1991 includes the unconsumed coal from 1990. If it didn't, if country Q imported no coal, obviously B would be impossible since you can't consume more than you have of something. If Country Q produced 6 tons in 1991, and consumed 8, then they HAD to have at least 2 left over from 1990 (this is our 1990 figure) meaning that the 1991 figure is 0, smaller than 2.

Root for your explaination.
Now I see how B is correct.

gmat740 wrote:Hello friends,

About a month back when I gave my GMAT exam, I encountered many CR questions which were above the OG-Level. I felt a need for thread which can be complied to have some really good CR's.
I am going to start this thread, basically I will be posting questions mostly from LSAT sets, and if they are from somewhere else I would quote the source as well.

I believe this to be a one stop collection of CR's for practice.I would post the OA after a little discussion.

Please State the reason for choosing a particular answer and rejecting others. That would help everyone to develop strategies for attacking CR's

D is the only one that does not really weaken the argument. how does whether or not a constituency is opposed to increasing local taxes affect the burden on those who will endure the bus fare hike? not at all. any argument you create would be out of scope and require assumptions not there.

OA-B

Below is the Explanation :

First look at the wrong choices:

(A), (C), (D), (E) The tally represents a comparison between the amount of coal mined and consumed. Any change in the tally from year to year therefore represents a change in this comparison. All of the wrong choices offer unsupported comparisons between one of the elements across years; in other words, mining in 90 vs. mining in 91, or consumption in 90
vs. consumption in 91. But all we have is information on the tally, a number that includes both factors. Without raw numbers, we can’t tell how the consumption numbers compared from 1990 to 1991; we need to know the amount mined before making the judgments in (C)
and (D).
The opposite holds for (A); we need the consumption figures before concluding how much was mined in 90 as opposed to 91. (E) has an even greater problem: it introduces a new concept—the first half of 90 and 91—which we know nothing about.

Important tip :We must assume that the term “total available coal supplies” refers to the cumulative stockpile carried over from year to year. That way, we can rightly infer (B) given the decrease in the tally from 1990 to 1991

The tip has already being explained by myohmy with help of certain examples. Please refer to her posts.

Questions of these kind make things difficult because all the answer choices look the same, you can't just use the POE to reach the correct answer.You must have a firm grasp of what is being talked about.

Hope this Helps

Assumption Question

gmat740 wrote:Assumption Question

IMO C .... if C was not true, directly affects the conclusion.

Although I have also chosen C as the answer, I was wondering if D can be the answer as well ?