Logical reasoning PrepTest 104 · Section 4 · Question 9

Question prompt

The only physical factor Remaining source text redacted.
Why the credited answer is right

Credited answer: E

The notes below walk through why it fits the stem and how to eliminate the rest.

Argument or Facts

Argument

Valid or Flawed

Flawed

Question Type

Strengthen with Necessary Premise Questions

Stimulus Summary

Problem - Fuel weighs too much for us to be able to go to Mars and back, and only weight prevents this trip
Solution - A new device that lets fuel be made on Mars
Conclusion - We can go to Mars!

Answer Anticipation

The stimulus here falls into a common pattern - a Problem/Solution argument. And it doesn’t have a variation on that pattern - it’s a straightforward presentation of a problem, along with a solution that the author believes will work!
When that’s the case, we should check to see if the proposed solution actually resolves the problem that’s noted. Here, the problem is one of weight - “only” weight prevents a human journey to Mars.
Up until recently, fuel was too heavy to make the trip possible. However, a new device has been invented that allows the return fuel to be made on Mars. That should substantially cut down on the amount of fuel needed, and thus lower fuel weight!
However, the problem wasn’t fuel weight specifically - it was weight. While the new device allows for rockets to carry less fuel, the device itself must weigh some amount. The argument is assuming, then, that the device itself isn’t heavy enough that it prevents the journey to Mars from happening, even with less fuel being required.
Let’s find an answer that discusses the weight of the device, and then ensure that it’s phrased in a way that makes it a necessary premise.

Answer choices

  1. A
    The amount of fuel Remaining source text redacted.
    Why choice A is not credited
    The amount of fuel doesn’t need to be the same for the argument to work. As long as the amount of fuel decreases enough to allow the weight to be low enough to make the trip physically viable, the argument can hold together.

  2. B
    The fuel manufactured from Remaining source text redacted.
    Why choice B is not credited
    There’s no indication that the fuel’s composition matters here - what matters is the weight, and we don’t know how the composition plays into that.

  3. C
    The device for manufacturing Remaining source text redacted.
    Why choice C is not credited
    The space taken up by the device doesn’t matter; what matters is its weight.

  4. D
    A conventional spacecraft equipped Remaining source text redacted.
    Why choice D is not credited
    First, the argument is about whether it’s possible, not affordable, to fly to Mars. Second, even if cost was a factor here, the argument doesn’t require the new ship/device to be about the same cost as a traditional ship - just not so much more expensive as to make it cost prohibitive.

  5. E
    The device for manufacturing Remaining source text redacted.
    Why choice E matches the stem
    This answer establishes that the device weighs less than the fuel and tanks for a conventional ship. If the device weighs the same amount, then there’s no weight savings in switching to it, and thus the problem isn’t addressed. As such, this answer is a necessary premise of the argument. (Note that it’s not sufficient, as the device would have to save enough weight to make it physically possible for the trek to work, which this answer doesn’t establish.)

What this tests

Question analytics

Based on historical answer selection rates for this question.

Answer choice distribution

  1. A 11%
  2. B 7%
  3. C 2%
  4. D 1%
  5. E Credited 79%

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Discussion

  • Why is A wrong? 1 reply

    Started by nathanielpfitzpatrick

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