to the top

#18 - In experiments in which certain kinds of bacteria were

Dave Killoran
PowerScore Staff
PowerScore Staff
Posts: 3169
Joined: Fri Mar 25, 2011 1:18 pm
Points: 3,165

Hi LSATNoobie,

Let me go backward here. First, the conclusion of "None" means that there is no conclusion that can be drawn. Literally, we don't know anything from combining the two prior statements. I'll go back and change that wording so it's clearer :-D

Second, the problem with answer choice (C) is that it doesn't work, so we are looking at a combination that is flawed. That makes the analysis more tricky, because you're showing the failure of (C) and why it doesn't produce the conclusion in the stimulus. So let's walk through it once more and try to make it clearer.

Basically, you have a Justify question, so to see if the answer works, you have to have pass through the Justify Formula:

    Premises + Answer Choice = Conclusion

    And just for reference:

      Premise: [some] genetic mutation is random
      Correct answer: ?
      Conclusion: all genetic mutation is random

      Now, we need the right answer to combine with the premise to force the conclusion.

So let’s apply that to (C):

    Premise in this problem: “[some] genetic mutations occurred at random in the populations.”

    Answer choice (C): “If all genetic mutations in bacteria are random, then all genetic mutations in every other life form are random also.”

The resulting conclusion from combining the two above: there is no valid conclusion that can be drawn. It’s an “if” statement in the answer choice, and we don’t know that we have the sufficient condition activated because "some" isn't enough to make that happen. So, we can't draw the conclusion made in the stimulus, and this answer fails to make the Formula work.

I tried to use an example that mirrors that with my football players example:

    Premise in this problem: “Some high school football players are athletic.”

    Answer choice (C): “If all high school football players are athletic, then football players at every level of the sport are athletic.”

    Conclusion: there is no valid conclusion that can be drawn

Let me try a different example, that gets to the heart of the issue without following the exact form of the argument the way I did with my example. In this case, I'll use rich or poor as the basis just to keep it simple:

    Stimulus: Some of us are rich, therefore all of us are rich.

    Answer choice (A): Either all of us are rich or none of us are rich.
    Answer choice (C): If All of us are rich, then the whole world is rich (this is imperfect, but let's go with it)

Now run each through the formula just to see how it works:

    Answer choice (A)

    Premise: Some of us are rich.
    Answer choice (A): Either all of us are rich or none of us are rich.

    Conclusion: All of us are rich

Ok, perfect, that worked. When we combined the answer choice with the premise, it produced the same conclusion as in the stimulus. This is the correct answer!

    Answer choice (C)

    Premise: Some of us are rich.
    Answer choice (C): If all of us are rich, then the whole world is rich.

    Conclusion: No conclusion can be drawn.

We only know that some of us are rich, but the sufficient condition in the answer is "all," and we don't know that for sure. so, the sufficient isn't activated, and we can't draw any absolute conclusion. Thus, this answer does not produce the same conclusion as in the stimulus.

Please let me know if that helps. Thanks!
Dave Killoran
PowerScore Test Preparation

Follow me on Twitter at
My LSAT Articles:
PowerScore PodCast:
LSAT Leader
Posts: 50
Joined: Mon Sep 18, 2017 5:12 pm
Points: 50

That was the best answer I have ever received for any question I have ever asked in life. Thank you so much haha.
LSAT Leader
Posts: 32
Joined: Wed Jun 27, 2018 12:01 pm
Points: 32

Dave Killoran wrote:Exactly. (C) is a brilliant answer because it contains the element you want to produce, but it contains it in a manner that doesn't allow you to produce that result.

Make sure you understand this question perfectly—it is one of my all-time favorites for understanding how the whole Justify idea works on this test!

I see what you are saying. It definitely illustrates the point.

I feel like I actually learned something profound when I came across this question. I got it wrong - A and C were the contenders.