Self-study
Leachate is a solution, frequently highly contaminated, that develops when water permeates a landfill site. ██ ███ ████ ██ ███ ████████████ ████████ ██ ████ ███████ ██ ████████ ████ ███ ████████ ██████ ████ ███ ████████████ █████████ ██ █████████████ ███████████ █ ██████ ████ ██ █████ ███ █████████ ██ █████████ ████ ████████ ████████ ██ ████ ████████ ██ ██████ █████████ ███████ ███ ███ ███ ██████ ██████ ███ ███████ ██ ████████ ███ ██████ ████████████ ██████
The Stimulus' Claims Distilled
In Must Be True questions, we can just treat the stimulus as a big ol' list of rules – 10 commandments style – any one of which could hold the key to the correct answer. The core skills tested in this question are properly translating the biconditional claim (marked with *) and understanding the limits of various quantifiers (I'll bold those terms). Here are the stimulus' claims broken down exhaustively and translated into logic-friendly phrasing:
- Leachate is a solution
- Leachate is sometimes highly contaminated
- Leachate develops when water permeates a landfill site
- If the landfill overfills, leachate escapes*
- If leachate escapes, the landfill has overfilled*
- Most of the time when leachate escapes, we can't predict how much will escape
- We must figure out how to dispose of leachate
- Most landfill leachate goes to sewage plants
- Some sewage plants are not capable of handling highly contaminated water
That's a lot of claims packed into four sentences! With such a broad field of possible right-answer sources, process of elimination is your best bet – run once through the answers noting promising contenders and eliminating any clearly-wrong choices, then cross-reference the remaining answer choices against the stimulus.
12.
Which one of the following ███ ██ ████████ ████ ███ ████████
a
The ability to ███████ ███ ██████ ██ ████████ ████████ ████████ █████ ████ █████ ███ ████████ ████████
The stimulus does tell us the amount of leachate that escapes is
b
If any water █████████ █ █████████ ████████ ████ ██████ ████ ███ ████████████
This mashes up two unrelated claims. The stimulus tells us:
- Leachate develops when water permeates a landfill site
- If the landfill's capacity to hold liquids is exceeded, leachate will escape into the environment
So both of (B)'s clauses reflect text in the stimulus – it's just that those pieces aren't connected by an "if, then" relationship.
c
No sewage treatment ██████ ███ ███████ ██ ████████ █████████
This is a much too strong restatement of the stimulus' claim that not all sewage plants are capable of handling the highly contaminated water. Properly translated, that claim reads:
Some sewage treatment plants are not capable of handling leachate.
d
Some landfill leachate ██ ████ ██ ██████ █████████ ██████ ████ ███ █████████ ██ ████████ ███
The plants incapable of handling leachate aren't necessarily receiving any leachate.
The stimulus tells us most leachate is sent to sewage plants of some description. The stimulus also tells us there are some sewage plants that can't handle leachate. None of the stimulus' claims prevent us from sticking to the sewage plants that can handle leachate.
e
If leachate does ███ ██████ ████ █ ████████ ████ ███ ████████████ ████ ███ ████████████ ████████ ██ ████ ███████ ███ ███ ████ █████████
The support for (E) comes from the stimulus'
- If the landfill overfills, leachate escapes
- If leachate escapes, the landfill has overfilled
Both these claims act as normal conditionals, meaning (among other things) that they can each be expressed in the contrapositive:
- If leachate doesn't escape, the landfill hasn't overfilled
- If the landfill doesn't overfill, the leachate won't escape
That bolded piece matches (E).