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Difficulty: MediumIdentifying Unstated Assumptions

In an effort to lower operating costs, the municipal transit authority of Oakhaven plans to replace its entire fleet of diesel-powered buses with electric buses. Management projects that this transition will significantly decrease total annual maintenance costs for the transit system, because electric buses have fewer moving mechanical parts than diesel buses do.

Which of the following is an assumption on which the municipal transit authority's projection depends?

  1. A
    The electricity required to charge the new electric buses will be generated entirely from renewable energy sources.
  2. B
    The transit authority will not experience any passenger fare revenue losses during the period when the bus fleet is being replaced.
  3. The ongoing maintenance costs for the electronic and battery components of electric buses will not exceed the savings achieved from having fewer mechanical parts.Answer
  4. D
    Diesel bus manufacturers will increase the cost of replacement parts for diesel buses over the next several years.
  5. E
    The municipal transit authority currently spends more on fuel each year than it spends on bus fleet maintenance.

Answer

The ongoing maintenance costs for the electronic and battery components of electric buses will not exceed the savings achieved from having fewer mechanical parts.
The argument concludes that total annual maintenance costs will decrease because electric buses have fewer moving mechanical parts. For this to hold true, any new or existing maintenance costs associated with non-mechanical systems (such as batteries, software, and electrical wiring) must not outweigh the savings realized from reduced mechanical maintenance. If non-mechanical maintenance expenses exceed those mechanical savings, the overall maintenance budget will not decrease.

Step-by-Step Solution

1
Deconstruct the argument into premise and conclusion.
Premise: Electric buses have fewer moving mechanical parts than diesel buses. Conclusion: Replacing the fleet with electric buses will significantly decrease total annual maintenance costs.
Isolating the premise and conclusion reveals the scope gap between mechanical parts and total maintenance costs.
2
Identify the underlying logical gap.
The author assumes that savings gained from having fewer mechanical parts will not be offset or surpassed by new non-mechanical maintenance expenses specific to electric buses.
Total maintenance costs encompass all components of a vehicle, not just mechanical ones.
3
Apply the Negation Test to verify the assumption.
Logical Negation: Non-mechanical maintenance costs WILL exceed the savings achieved from having fewer mechanical parts. Outcome: If this negated statement is true, total maintenance costs will increase or stay the same, completely destroying the conclusion.
A valid assumption must be necessary for the conclusion to hold true.

Key Concept

Identifying Unstated Assumptions
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Topics

Identifying Unstated Assumptions

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