Logical reasoning PrepTest 114 · Section 2 · Question 25

Incorrect. The argument doesn't assume that Earth is representative of life—sustaining planets, or that being Earth—like is sufficient to have life. It's assuming that the solar system is representative in that ~1/9 planets will be able to sustain life, whether or not they're Earth—like. It also talks about one planet qualifying as fit to sustain life, but that could describe a variety of types of planets, of which Earth is just one.

Corect. Argument or Facts:
Argument

Valid or Flawed:
Flawed

Question Type:
Errors in Reasoning

Stimulus Summary:
Our solar system — Only 1/9 plants can sustain life (RIP Pluto)
But, the universe is massive . . .
So there's a lot of life out there!

Answer Anticipation:
The argument extrapolates from what is true in our solar system to what must be true of the universe generally. However, it's possible that our solar system is unique, or it's at least exceptionally rare in having 1/9 planets that can sustain life. The argument is assuming that our solar system isn't particularly special—that it's generally representative of other solar systems as far as the frequency of life—sustaining planets is concerned.

Since the question stem asks us what the argument "presumes . . . without providing justification" which is just a fancy way of saying "assumes" let's find an answer stating that assumption.

Answer Explanation:
The argument assumes that the ratio of life—sustaining planets in our solar system is representative of other systems throughout the universe, thus allowing our 1/9 ratio to pan out other places, leading to a very large number of aliens. This answer states the assumption of the argument, so it's the correct answer.

Key Takeaway:
When an argument uses what's true in one situation to generalize to all situations, that's a bad generalization. This can be viewed through a comparison or a sampling lens—it's assuming that the situation mentioned is representative or similar to the average.

Incorrect. The argument doesn't assume that these conditions are well understood, just that they're identifiable. We can identify something that we can't understand—a lot of science comes down to making an observation and then figuring it out later!

Incorrect. The argument brings up "qualif[ications] . . . to sustain life." It could be that these qualifications are limited to Earth—like qualities or Earth could just fall into one of many categories of life—sustaining types. As such the argument doesn't assume that the life—sustaining planets are like or unlike Earth outside of being able to sustain life.

Incorrect. Since the argument deals with a ratio, it's not required to assume that other planetary systems have 9 planets. It's possible some have, say, 18, and it's expected that 2 can sustain life; or 23 and 2—3 can sustain life.