Logical reasoning PrepTest 138 · Section 3 · Question 20

Incorrect. This is a very tempting answer choice—if you were torn between two answers, it should have been this one (D). However, there are a few issues with it. First, it doesn't reference an opposing point at all, and the Scientist's argument was set up as a rebuttal. Second, the argument skips over the whole implication portion of the argument. Third, the reasoning connects an "overwhelming" likelihood that an event would occur during our lifetime, not a certainty as this answer suggests. This answer has elements that match up with the stimulus, but the problem is that there are too many elements in the stimulus that don't get referenced here that are key to how the argument proceeds, so this answer is wrong.

Incorrect. The conclusion here is that humans probably won't colonize the galaxy. The premises have to do with currently living humans being representative, and there not being a galaxy-wide colonization effort on the horizon of our lifetimes. The conclusion doesn't contradict either of those premises, so this answer is incorrect.

Incorrect. The Scientist uses present facts to make a prediction about the future, so she doesn't assume that such premises can't serve as a basis for such a prediction.

Correct. Argument or Facts:
Argument

Valid or Flawed:
Flawed

Question Type:
Methods of Reasoning

Stimulus Summary:
Background - Humans like to explore/colonize
Theory - The galaxy will have trillions of humans throughout it
Implication - The vast majority of humans would be alive at this time
Scientist - We are representative humans, so we should be alive at this time. We're not, so it probably won't happen.

Answer Anticipation:
This is a doozy of a question, so let's start by sketching out the basics of it and then dive into the details.

The basics are that the Scientist here contradicts a theory—she doesn't just say that it's unsupported, but rather that its conclusion is very unlikely to ever happen.

Now, to dig into the details—how does she do this? Well, she starts digging into the implications of that theory. If there are trillions of humans alive at that time, then they'll make up the vast majority of the humans who ever lived (after all, there are currently only a few billions of us). And since that means a "representative" human would be alive at that time, and we have no reason to think we're representative, then we would be alive at this time if it were to come to pass. Since we're not, it's unlikely to happen.

Say what now?

This is a complicated argument, no doubt about it, so let's step away from the content and build off the basics with the logic of the argument. Starting with the opposing point, the author pivots using an interesting phrase—"If soÉ" That brings up an implication of the theory. So if the theory is true, then this other thing is, as well. And the implication of the argument would itself mean that it's likely something else is true (that we'd be alive during the time period of colonization).

Then, since that likely thing isn't true, the author concludes that the theory is itself almost certainly wrong.

That's a long, complicated road we just went down, but we're at the goal line now—we need to find an answer that states the author points out that an implication of a theory is unlikely to be true, so the theory itself is almost certainly wrong.

Answer Explanation:
The vast majority of people will get this question down between (A) and (D). When you're torn between two answers, it's important to compare them to each other. Both answers talk about an event not happening. However, (D) adds the context in the argument—it's an implication of a theory ("on a given hypothesis"), and it's a likelihood ("odds are overwhelming"). These elements in (D) match the stimulus better than answer choice (A). Additionally, this answer reflects the conclusion better by stating that the Scientist rebuts a hypothesis, which has more context than (A) while still conveying the same idea. This answer reflects the argument better than the other answer, and since this question is asking us to describe the argument, that's a reason to pick it. (A) is off enough and (D) has all the context, so this is our answer.

Key Takeaway:
When you're torn between two answers that are similar, compare them to each other to see what's going to determine which is right and which is wrong. In general, the answer that is closer to the stimulus is correct, so identify these relevant differences and then compare them to the language in the stimulus.

Incorrect. The opposing point is making a prediction about the future based on human tendencies (humans like to explore/colonize, so they're likely to do that throughout the galaxy in the future). The author is basing her prediction about the future not on human tendencies but rather on representativeness of a sample.