LR Question 21 Explanation, by LSATHacks
QUESTION TEXT: If the city starts requiring residents to…
QUESTION TYPE: Must Be True
FACTS:
- If the city requires sorting, many residents will put recyclables in their regular garbage.
- If residents put recyclables in their garbage, more recyclables will be buried in the landfill.
- The sanitation department can’t stay within its budget unless the city requires sorting.
ANALYSIS: It sounds like either more recyclables will end up in the landfill or the sanitation department will exceed its budget.
We have no idea what happens if the department exceeds its budget.
___________
- We don’t know. We know many residents won’t recycle. ‘Many’ could mean almost all residents (or even all). So maybe only 10% of residents will keep recycling after the change.
- Who knows? Some residents might continue to recycle, but screw up and avoid sorting the recyclables they put out for pickup.
- We have no idea how much landfills cost. There’s no way to compare this to the cost of sorting.
- CORRECT. If the sanitation department stayed within budget, it’s because the city required sorting. Sorting would cause more recyclables to be sent to landfill.
- Not necessarily true. We know the department will definitely exceed its budget without the sorting requirement. But it might exceed its budget even with sorting. Sorting was a necessary condition for meeting the budget, not a sufficient condition.
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So for D, we say if sanitation stayed within budget then amount of recyclables going to landfill is increased and that’s because the city put through the sorting requirement. Yet for answer choice E we say that isn’t a logical string of theory. In particular.
So from “If the sanitation department stayed within budget, it’s because the city required sorting” to “it might exceed its budget even with sorting”.
I imagine my confusion has to do with the ending of answer explanation on E to do with sufficiency versus necessity but what am I missing here? How is it you can make a reasonable assumption for D but that same assumption is not doable for E?
Here’s what the stimulus tells us:
(1) City requires residents to sort recycling –> More recycling in with regular garbage –> More recycling in with landfill
(2) The sanitation department won’t stay on-budget unless the sorting requirement is implemented. Here’s what the diagram looks like:
On-budget –> Sorting implemented
If we chain these two points together, we get: On-budget –> Sorting implemented –> More recycling in with regular garbage –> More recycling in with landfill.
That’s why (D) is correct. It follows the chain. It says On-budget –> More recycling in with landfill.
(E) looks like this:
City implements sorting requirement –> On-budget
That’s the reverse of point (2). We can’t reverse the necessary and sufficient conditions unless we also negate them both (i.e. take the contrapositive). Note that in (2), sorting is a necessary condition of being on-budget. That means that maybe even if sorting is implemented, the city will exceed its budget.