amount of coal

[ranell]

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.

[ranell]

The OA will be given after discussions.

[gmatmachoman]

total available coal supplies
==
total amount mined- total amount consumed.

B,C,E are ruled out.

We are left with A & D
It can be either of A or D depending on which is constant.Here no data is given about whether the amt to be mined or the amt to be consumed between the years to be constant.that creates the dilema of opting A or D

Since it says they are not importing or exporting,somepoint of time their resources shall deplete.If teh rate of mining is constant then amt of coal mined in 1991 is less than 1990.
By that IMO A is stronger than D.

My vote goes to A


Iam damn eager to c the OA and comments!!1

[rohan_vus]

Has to be B ..You need to take care of cumulative amounts of coal .

A could be true but here point is 'must be true' answer. It could be that in 1990 less coal was mined but even less was consumed .. so you get more unconsumed coal left over than 1991..So A cant be must be true answer

[gmatmachoman]

Yeah ,But Once again we are making assumptions.Dont u think so?

[gizemystery]

I think it's B too.

In 31st Dec 1990 they have X and in 1991 they mine Y and spend Z. so in 31DEC91 they have X+Y-Z and it's smaller than X... hence Z must be greater than Y. or more coal consumed than mined in 1991.

[srivas]

Total available coal = Total Mined - Total Consumed(Total amount of coal tmined throughout the country but not consumed).

So IMO is B

[kaulnikhil]

IMO B .. took a lot of time

1990
mined consumed not consumed
100 30 70
now in 1991 this 70 will be carry forwarded
Mined consumed notconsumed


70+ 10 20 60
70+ 30 40 60
70 + 100 110 60

[pandeyvineet24]

B should be the answer

[ranell]

B is the right answer

[heshamelaziry]

I got B after 2 minutes 20 seconds

[karthikpandian19]

From the argument how is that it is assumed the coal supplies are cumulative and not year on year basis.

[GMATGuruNY]

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.

By definition, the amount of coal AVAILABLE is equal to the TALLY at the end of the PREVIOUS year + THE INCREASE OR LOSS from the CURRENT year.

At the end of 1990, TALLY = mined - consumed = x.

In order for the value of x to DECREASE in 1991, the tally in 1991 -- in other words, the value of (MINED IN 1991 - CONSUMED IN 1991) -- must be NEGATIVE.

Thus, it must be true that CONSUMED IN 1991 > MINED IN 1991, supporting answer choice B:
In Country Q, the amount of coal consumed in 1991 was greater than the amount of coal mined in 1991.

The correct answer is B.

[karthikpandian19]

Mitch,

Each December 31 in Country Q, a tally ...., the total amount of coal that has been mined throughout the country but not consumed.

I was initially confused with the usage of BUT in this sentence, that i accounted that "consumption" must not be taken into account for the equation.
But as per the explanation, it functions as subtraction in the equation

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.

By definition, the amount of coal AVAILABLE is equal to the TALLY at the end of the PREVIOUS year + THE INCREASE OR LOSS from the CURRENT year.

At the end of 1990, TALLY = mined - consumed = x.

In order for the value of x to DECREASE in 1991, the tally in 1991 -- in other words, the value of (MINED IN 1991 - CONSUMED IN 1991) -- must be NEGATIVE.

Thus, it must be true that CONSUMED IN 1991 > MINED IN 1991, supporting answer choice B:
In Country Q, the amount of coal consumed in 1991 was greater than the amount of coal mined in 1991.

The correct answer is B.

[ihatemaths]

so basically we have to infer "COAL that is left off" isn't it ?