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If a municipal water treatment plant utilizes ultraviolet purification, it must also employ continuous spectral monitoring. Any facility that employs continuous spectral monitoring requires at least two full-time optical engineers on staff. However, some municipal water treatment plants in the Oakhaven region do not require at least two full-time optical engineers on staff.

Which of the following logically follows from the statements above?

  1. A
    Any municipal water treatment plant that requires at least two full-time optical engineers on staff utilizes ultraviolet purification.
  2. B
    Municipal water treatment plants that do not utilize ultraviolet purification do not employ continuous spectral monitoring.
  3. C
    Ultraviolet purification is more expensive to maintain than other water treatment methods used in the Oakhaven region.
  4. Some municipal water treatment plants in the Oakhaven region do not utilize ultraviolet purification.Answer
  5. E
    Most municipal water treatment plants in the Oakhaven region do not employ continuous spectral monitoring.

Answer

The correct answer is the statement that some municipal water treatment plants in the Oakhaven region do not utilize ultraviolet purification.
The stimulus establishes a conditional chain: if a plant uses ultraviolet purification, it must employ continuous spectral monitoring, which in turn requires at least two full-time optical engineers (UV -> Spectral -> 2+ Engineers). The contrapositive is that if a plant does not have at least two optical engineers, it cannot use ultraviolet purification (~2+ Engineers -> ~UV). Since we are told that some plants in the Oakhaven region lack these engineers, it logically follows that these specific plants cannot be utilizing ultraviolet purification.

Step-by-Step Solution

1
Identify and diagram the conditional statements in the stimulus.
Ultraviolet (UV) -> Spectral Monitoring (SM), and Spectral Monitoring (SM) -> 2+ Engineers (2E).
Breaking down the formal logic reveals the directional relationships between the requirements.
2
Combine the conditional statements into a single logical chain.
UV -> SM -> 2E.
Connecting the conditions allows for broader logical deductions across the entire stimulus.
3
Determine the contrapositive of the full conditional chain.
If ~2E -> ~SM -> ~UV.
The contrapositive is logically equivalent to the original chain and is necessary to apply the final negative premise.
4
Apply the factual premise about Oakhaven region plants to the contrapositive chain.
Since 'some' Oakhaven plants have ~2E, these same plants must follow the chain to ~UV.
This yields the only definitively provable inference from the provided text.

Key Concept

Must Be True - Conditional Chaining and Contrapositives
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