Each December 31 in Country Q, a tally is made of the country’s total

Question

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.

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.
(B) In Country Q, the amount of coal consumed in 1991 was greater than the amount of coal mined in 1991.
(C) In Country Q, the amount of coal consumed in 1990 was greater than the amount of coal consumed in 1991.
(D) In Country Q, the amount of coal consumed in 1991 was greater than the amount of coal consumed in 1990.
(E) In Country Q, more coal was consumed during the first half of 1991 than was consumed during the first half of 1990.

vineet474 · Accepted Answer

Dude no need to thank me for the kudos. You deserved it actually when you explained the question with an example. You keep explaining like this and I'll keep sending my gestures. :wink:

Ok ..I got your point when you say that " it maybe true but not necessary that it MUST be true". Here's an example to prove this one. 1990 : Coal Mined = 10kg Coal consumed = 8kg Coal reserve= 2 kg 1991 : Coal Mined = 2kg Coal consumed = 3.5kg Coal reserve= 0.5 kg (considerably less than 1990 as mentioned in the question) Hence, it is not necessarily true that coal consumption of 1991 was greater than that of 1990. However, the point that coal consumed in 1991 is ALWAYS greater than the coal mined in 1991 hold true EVERY TIME. Explained it for anyone who might be interested in this post. :-D

Cheers, -V

craky · Answer

This seems odd. I would pick B.

As it states:
  In 1991
that amount was considerably lower than it had been
in 1990.

That means that spare supplies of coal were lower in 1991 than in 1990, therefore by constant mining, in 1991 they consumed more coal: either mined in that year or from reserves from 1990.

vinzycoolfire · Answer

i got it now! B is indeed correct. if in 1990 10 kilos are produced out of which 8 kilos are consumed , then the number for 1990 would be 2 kilos. the number for 1991 to have less than that of 1990(less than 2 kilos), it should have a consumption large enough to nullify the amount mined in 1991 and then some more (this is because the figure for 1991 would be calculated by coal mined in 1991 - coal consumed in 1991 + amount left in 1990).
i shud hav read the choices carefully :wall

Zatarra · Answer

If the statements above are true, which one of the
following must also be true on the basis of them?
Pls Pay attention to Must 
Its not a could be true question
What if the consumption was less than the mined quantity (and the amount left over after the consumption is less than the amount left over the previous year )and not more than the mined quantity
B is answer to a Could Be True Question.ie:It doesnt have to necessarily be True

vinzycoolfire · Answer

no dude it is 3 kilos. 2 kilos of 1990 and 1 kilo in 1991. it is cumulative. why? because the 2 kilos(of 1990) will also be available for consumption, u can't take that out of the equation as the question does not define total coal available as amount mined PER year - amount consumed PER year. it just states "the total amount of coal that has been mined throughout the country but not consumed". so total available coal in 1991 should include amount left out in 1990 + amount left out in 1991.

now this is less than the 1990 figure, so obviously the left out amount in 1991 should be negative or in other words consumption is more than amount mined.

hope this helps.

now this is less than the 1990 figure, so obviously the left out amount in 1991 should be negative or in other words consumption is more than amount mined.

hope this helps.

vineet474 · Answer

I understood the points raised by both parties here but just curious to know that if consumption was greater in 1991 than that of coal mined (1991), then answer choice D automaticaly becomes true. Isn't it??

Please shed some light on this issue.

Thanks
-V

Please shed some light on this issue.

Thanks
-V

vinzycoolfire · Answer

thanx vineet474 for the kudos. :-D

the point you are raising about D is not correct. if the consumption of 1991 is more than coal mined in 1991 it is sufficient to explain the scenario. no need for consumption of 1991 to be more than consumption of 1990(it maybe true but not necessary that it MUST be true). if still in doubt try it with an example and let me know your doubts. will try to help.

ShashankDave · Answer

Please check option B. It is stated as the OA.

The stimulus states that Coal Available = Coal Mined - Coal Consumed

How can more coal be consumed than be mined in the same year?

Other than this option, every other option can be proven wrong. Please check both the question and its OA.

Thanks

GMATNinja · Answer

This is possible because Country Q can have a stockpile of coal leftover from previous years. Perhaps Country Q had a huge supply of coal stored up in 1990. Theoretically, they could then use the coal from that supply in 1991, reducing or eliminating the need to mine for new coal.

The OA (B) is correct.

I hope that helps!

abhishekdadarwal2009 · Answer

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.

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.
 (B) In Country Q, the amount of coal consumed in 1991 was greater than the amount of coal mined in 1991. 
(C) In Country Q, the amount of coal consumed in 1990 was greater than the amount of coal consumed in 1991.
(D) In Country Q, the amount of coal consumed in 1991 was greater than the amount of coal consumed in 1990.
(E) In Country Q, more coal was consumed during the first half of 1991 than was consumed during the first half of 1990.

The coal left without consumption is counted in the end of the year.
This extra coal is then consumed in the next year.

Option B is correct because it says that this years coal left is less than that left last year, this means that the production stays stable but the consumption has increaed because the left out coal is less than the coal left last year so that clearly measn the consumption has increased

abhishekmayank · Answer

Options B is correct. But it doesn't look like a "MUST" be condition, as the question is asking for. There could be other situation also in which it happens to be : the available coal supplies in 1991 < available coal supplies in 1990.

Such as :

Coal mined in 1990 = Coal mined 1991
Coal consumed in 1990 < Coal consumed in 1991

Such as :

Coal mined in 1990 = Coal mined 1991
Coal consumed in 1990 < Coal consumed in 1991

unraveled · Answer

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.

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. - WRONG. Both side possibilities exist.
(B) In Country Q, the amount of coal consumed in 1991 was greater than the amount of coal mined in 1991. - CORRECT.
(C) In Country Q, the amount of coal consumed in 1990 was greater than the amount of coal consumed in 1991. - WRONG. Again both side possibilities exist.
(D) In Country Q, the amount of coal consumed in 1991 was greater than the amount of coal consumed in 1990. - WRONG. 100 in 1990 and 1000 in 1991. Still, the left amount of coal considerably can be lower in 1991 than what it was in 1990. However, the reverse is also possible - 1000 in 1990 and 100 in 1991. The latter case is also possible because mined coal could have been so high in 1990 that higher consumption in 1990 relative to 1991 was possible.
(E) In Country Q, more coal was consumed during the first half of 1991 than was consumed during the first half of 1990. - WRONG. We can't be sure.

A difficult one.
The best part is that it asked for a 'must be true' not 'sufficient', otherwise it would have left opened so many choices. 
OR 
May be choices where they would have been far more vague.

So what do we do when after consumption of mined coal the amount of coal left in 1991 was considerably lower than it had been in 1990. 
Possibly, no coal is mined in 1991 with leftover of 1990 is used. But is it necessary such that no other possibility exists. No!! - there can be other possibilities still.
What makes B difficult is that it compares amount of coal consumed in 1991 to the amount of coal mined in 1991, which leads one to believe that such a comparison is irrelevant or at best not possible.

Consider this:
1990:
Mined - 1000, Consumed - 900, Left - 100

1991: 
Mined - 1000, Consumed - 990, Left -  110  (Not possible)
Mined - 100, Consumed - 90, Left -  110  (Not possible)
Mined - 1000, Consumed - 1090, Left -  10  (Possible)
Mined - 0, Consumed - 50, Left -  50  (Possible)
Mined - 0, Consumed - 10, Left -  90  (Possible)

Last one makes things difficult though. 
So, all in all, the consumption of coal has to be more than mined coal in 1991.

Answer B.

playerwellknown1 · Answer

Option B doesnt HAVE TO BE TRUE?
If option b is true , then Available supplies will always be negative. But it doesnt HAVE to be negative.

take this example. 
1990 Mined = 100 , used = 10 available = 90 (maybe everyone went on a holiday the whole year)
1991 mined = 90, used = 89 available = 1 
So the used doesnt HAVE to be more than mined

GMATNinja · Answer

The 90 available at the end of 1990 doesn't just disappear. The "1" available from 1991 represents the amount  added  to the supply in 1991. But at  the end  of 1991, the total available would be 91 -- so the example does not actually fit the statements in the passage.

I hope that helps!

VerbalBot · Answer

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Each December 31 in Country Q, a tally is made of the country’s total

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