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Question

Difficulty: MediumIdentifying Underlying Assumptions

A team of urban acoustic engineers evaluated several public plazas in major cities and observed that plazas constructed with porous travertine paving blocks exhibited significantly lower measured ambient traffic noise levels than those paved with dense granite slabs. The engineers concluded that replacing granite slabs with porous travertine paving in public plazas across the metropolitan area will reliably decrease ambient noise pollution throughout the surrounding urban neighborhoods.

Which of the following statements represent necessary unstated assumptions upon which the argument depends? Select all that apply.

  1. Differences in background traffic volume or proximity to major roadways were not the primary cause of the lower noise levels measured at the travertine-paved plazas.Answer
  2. The acoustic noise reduction achieved within the physical boundaries of a plaza extends into the surrounding urban neighborhoods.Answer
  3. C
    Porous travertine paving blocks are more cost-effective to install and maintain over a ten-year period than dense granite slabs.
  4. D
    Replacing granite paving with travertine will completely eliminate ambient noise pollution in the metropolitan area.
  5. E
    The dense granite slabs currently installed in municipal plazas actively reflect sound back into surrounding buildings.

Answer

The argument depends on assuming that background traffic differences were not the real cause of the lower noise levels observed, and that acoustic noise reduction within the plaza boundaries extends into surrounding urban neighborhoods.
The conclusion claims that travertine paving will decrease noise pollution in surrounding urban neighborhoods based on comparative observations of existing plazas. To validate this claim, the author must assume that alternative explanations (such as background traffic volume differences) were not the true cause of the observed noise reduction. Furthermore, the author assumes that the observed noise reduction inside the plaza extends to the broader surrounding neighborhood.

Step-by-Step Solution

1
Analyze the argument structure
Premise: Plazas paved with porous travertine have lower measured traffic noise than plazas with granite slabs. Conclusion: Replacing granite with travertine in city plazas will reduce ambient noise in surrounding urban neighborhoods.
Isolating the premises and conclusion clarifies the logical leaps made by the author.
2
Apply the Negation Test to identify necessary assumptions
Negating the statement regarding background traffic volume shows that if traffic differences caused the lower noise, travertine itself is not responsible, breaking the causal link. Negating the statement about noise extending beyond plaza boundaries demonstrates that if noise reduction is strictly confined to plaza interiors, surrounding neighborhoods will not benefit.
A statement is a necessary assumption if its logical negation causes the argument's conclusion to collapse.
3
Evaluate distractors
Financial cost considerations and total elimination of noise pollution go beyond the scope of the conclusion, while active reflection by granite is a helpful strengthening point but not strictly required for travertine to work.
Eliminating options that are out of scope, overly extreme, or merely helpful rather than required isolates the true assumptions.

Key Concept

Identifying Necessary Assumptions using the Negation Test
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Topics

Identifying Underlying Assumptions

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