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#35299
Complete Question Explanation

Must Be True—SN. The correct answer choice is (D)

The stimulus presents a fact set driven by conditional reasoning. Applying the Unless Equation to the last sentence, the phrase modified by “unless” becomes the necessary condition, whereas the remainder is negated and becomes the sufficient condition:
  • Sorting = Sorting requirement
    GR = Garbage recyclables
    LR = Landfill recyclables
    Budget = Sanitation department stays within budget

    Statement (1): ..... Sorting ..... :arrow: ..... Increase GR

    Statement (2): ..... Increase GR ..... :arrow: ..... Increase LR

    Statement (2): ..... Budget ..... :arrow: ..... Sorting
By combining these three conditional statements, we can infer that the amount of recyclables in landfills will have to increase if the sanitation department is to stay within budget:
  • Budget ..... :arrow: ..... Sorting ..... :arrow: ..... Increase GR ..... :arrow: ..... Increase LR
This prephrase is tremendously helpful in attacking the answer choices and immediately proves that answer choice (D) is correct.

Although the relationships described also contain elements of causation (“this will result in…”), the language in the second sentence suggests an inevitable, absolute outcome typical of a conditional relationship. Additionally, the causal reasoning in stimuli containing fact sets does not warrant the same level of scrutiny as does the conditional reasoning in them, especially when the latter suggests the presence of chain relationships (as is the case here).

Answer choice (A): The information contained in the stimulus cannot help us determine whether most of the city’s residents will continue to recycle after the sorting requirement is implemented. All we know is that many of them will put more recyclables in with their regular garbage. What proportion of residents continue to recycle is entirely unknown.

Answer choice (B): We cannot be certain if all of the city’s residents who recycle will actually comply with the sorting requirement, if implemented.

Answer choice (C): Granted, the annual cost of sorting recyclables is likely to decrease after the new sorting requirement is implemented, while the cost of sending garbage to the landfill will probably increase. However, we do not know the relative value of these two costs before the new requirement is implemented, which means that we cannot calculate their relative value after. It is entirely possible, for instance, that the annual cost of sending garbage to the landfill already exceeds the current cost of sorting recyclables.

If the sanitation department is to stay within budget, there is only one conclusion we can draw (assuming all other costs and revenues remain constant): the added cost of sending garbage to the landfill cannot exceed the savings that would result from not having city workers do the sorting.

Answer choice (D): This is the correct answer choice, as it matches the additive inference of the chain relationship outlined above:
  • Budget ..... :arrow: ..... Increase LR
Answer choice (E): This answer choice is incorrect, because it is a Mistaken Reversal of the third sentence:
  • Sorting ..... :arrow: ..... Budget
 Basia W
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#16701
Good evening,

I was hoping someone could help me with the chain to get to D- I chose E and I know realize that this is a mistaken reversal.

thank you for your help!

P.S how much diagramming on these sorts of diagrams would you recommend for test day?

Best,

Basia
 Emily Haney-Caron
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#16704
Hi Basia,

DEFINITELY diagram these kinds of questions on test day - it is essential for pretty much any S/N question type.

Here's my diagram:
requiring sorting :arrow: recyclables thrown away
not requiring sorting :arrow: not within budget
And then the contrapositive: within budget :arrow: required sorting

So we now know that if they stay within budget, it means they required sorting, which means recyclables were thrown away.
 Basia W
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#16710
Hello!

thank you for your explanation: I just had a question regarding the last part because the "sorting requirement for residents is implemented" comes after the unless wouldn't that make it the necessary condition?

Stay within budget :arrow: sorting requirement is implemented?

thanks,

Basia
 Basia W
  • Posts: 108
  • Joined: Jun 19, 2014
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#16712
Oh sorry- I just noticed that formed part of your contrapositive! :lol:

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