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Difficulty: HardDistinguishing Inferences from Assumptions and Speculations

An urban transit authority conducted a comprehensive survey of all commuter rail passengers traveling on Line X during peak morning hours. The survey established that every passenger who traveled with a monthly pass completed their journey in under 45 minutes. The survey also determined that 30 percent of all morning peak passengers on Line X did not travel with a monthly pass, and that no passenger without a monthly pass completed their journey in under 30 minutes.

If the statements above are true, which of the following must also be true on the basis of them?

  1. At least some morning peak passengers on Line X took 30 minutes or more to complete their journey.Answer
  2. B
    Any morning peak passenger on Line X whose journey took under 45 minutes must have held a monthly pass.
  3. C
    Holding a monthly pass directly enables passengers to bypass transit delays and reduce overall travel time.
  4. D
    Passengers without monthly passes were delayed primarily by ticketing queues at origin stations.
  5. E
    The transit authority will increase the price of monthly passes to manage morning peak congestion.

Answer

The statement that at least some morning peak passengers on Line X took 30 minutes or more to complete their journey must be true.
The correct answer is strictly derived from combining two premises: 30 percent of peak morning passengers did not hold monthly passes, and zero passengers without monthly passes completed their journey in under 30 minutes. Therefore, all passengers within that 30-percent subset took at least 30 minutes (30 minutes or longer), guaranteeing that at least some passengers took 30 minutes or more.

Step-by-Step Solution

1
Analyze the explicit premises given in the stimulus.
Premise 1: 100% of monthly pass holders finished in under 45 minutes. Premise 2: 30% of total passengers did not hold a monthly pass. Premise 3: 0% of non-pass holders finished in under 30 minutes.
Inference questions require strictly factual evaluation without external assumptions.
2
Synthesize the facts regarding non-pass holders.
Since non-pass holders make up 30% of the total passenger population and none of them completed their trip in under 30 minutes, every member of this 30% group took 30 minutes or longer.
If a subset of passengers exists and none of them took under 30 minutes, then every passenger in that subset took 30 minutes or more.
3
Evaluate the options to distinguish a strict deduction from unstated assumptions and speculative claims.
The option asserting that at least some passengers took 30 minutes or more is guaranteed by the 30% group of non-pass holders.
A valid GMAT inference must be 100% true based strictly on the premises.

Key Concept

Distinguishing strict logical deductions (Must Be True) from unstated causal assumptions or speculative extrapolations.
Estimated Time:2m 0s
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Topics

Distinguishing Inferences from Assumptions and Speculations

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