Logical Reasoning

PT105 · S2 · Q24 Each December 31 in Country Q

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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.

Statements

On the last day of the year, Q tallies up how much total coal supplies they have (mined, but not consumed).

Last day of '91 had much lower supplies than last day of '90.

Q hasn't imported or exported coal since 1970.

Evaluate

Must Be True questions tend to involve conditional logic or mathematical comparisons. This appears to be the latter.

The last fact, that Q doesn't import or export coal, is seemingly just establishing that Q is a closed system. Any coal they mine, they use. Any coal they use came from their mines.

So if they have less coal in the bank account at the end of '91 than at the end of '90, what can we infer? Why did the coal account go down?

Did they start mining less? Did they start using more? Some combo?

The one thing we can say, if our bank account is lower on Dec 31 than it was on Jan 1, is that over the course of the year we spent more money than we earned.

Goal

So we should be able to say that during 1991, we consumed more coal than we mined.

24.

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

  1. In Country Q, more coal

    Not Necessarily

    It's possible that an equivalent amount of coal was mined in both years, and we just consumed more coal in 1991, thus lowering our coal supplies.

    17% picked this

  2. Correct

    In Country Q, the amount

    Why this is right

    Say that on Dec 31, 1990, we had 100 tons of coal supplies. We know that on Dec 31, 1991, we had considerably lower (let's say 70 tons of coal supplies). That means that during 1991 we consumed more than we mined; we spent more than we earned.

    Skill tested: Must be True · how this choice captures the argument's function is the move to repeat next time.

    46% picked this

  3. In Country Q, the amount

    Not Necessarily

    This is the flipside of (A). We know the two things that affect the coal supplies bank account are coal mined and coal consumed, but we're not sure the exact combo that dwindled our account during 1991. This answer is actually counterintuitive, in addition, because we would expect 1991 to be the year we consumed more coal (since we know 1991 ate into our coal savings account).

    6% picked this

  4. In Country Q, the amount

    Not Necessarily

    This is the same as (C), only they flipped it to the more intuitive idea that "more coal was consumed" in 1991. But it's possible that the same (or less) coal was consumed in 1991, and the reason the coal account went down is because we mined less coal in 1991.

    29% picked this

  5. In Country Q, more coal

    Out of Scope: first half

    We definitely don't have any information that would allow to derive definite truths about 1st half of 1991 vs. 1st half of 1990.

    1% picked this

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