Q18 - In experiments in which certain

[mleeker]

The argument seems pretty straight forward, I'm just having trouble with the answer choices. I can see how (A) is correct, but I'm having troubling understanding exactly why the other answer choices are incorrect.

[bbirdwell]

Utilize the extreme nature of the conclusion to your advantage -- it's very difficult to prove "all" anything...

Conclusion:
All mutation is random

Premise:
In this experiment, mutation occurred at random.

What would allow this conclusion to be true?
(A) Yep.

(B) So what?

(C) This is a conditional choice that doesn't help us much because we don't know if all bacterial mutations are random or not -- just the ones in this experiment.

(D) Ok... this doesn't help us get to ALL mutations being random.

(E) Same as D.

#officialexplanation

[weiyichen1986]

Hey, i chose C , here is my reasoning, but feel free to correct me.

C) basically lead to mutations in all forms are randoms.
If it is all random in every form, then isnt it true that it is all random?

[bbirdwell]

(C) is wrong because the argument doesn't say that all bacterial mutations are random. Thus, the condition (IF all bacterial mutations are random) has not been met. We only know about the bacteria in this one experiment, and that's the only kind of condition we can meet ("If the bacterial mutations in this experiment are random...") This would be a better choice if it said something like "The bacteria in this experiment are representative of all life."

[ottoman]

Can you explain the reasoning for A?

Thank you!

[ohthatpatrick]

Sure thing.

Remember the task of Sufficient Assumption:
Pick an answer that, when we add it to the premise(s), proves the conclusion perfectly

Premise:
(In certain experiments) genetic mutations occurred at random.
+
Choice (A):
All genetic mutations are random or no genetic mutations are random.
=
Conclusion:
All genetic mutations are random

Do you see how that conclusion results as an inference?

Suppose you give me a rule that says "All of Linda's friends are left-handed or none of Linda's friends are left-handed"

Now say we meet Roger, one of Linda's friends. If it turns out he's left-handed, then ALL of Linda's friends are left-handed. If it turns out he's not, then NONE of Linda's friends are left-handed.

That's how the Premise + Choice (A) ---proves--> Conclusion.

Don't worry that (A) is a CRAZY extreme idea. Sufficient Assumption is about thinking mathematically -- your job is just to find an answer choice that lets you PROVE (with no doubt whatsoever) that the conclusion is true.

Let me know if this doesn't make sense.

[ban2110]

Sure thing.

Remember the task of Sufficient Assumption:
Pick an answer that, when we add it to the premise(s), proves the conclusion perfectly

Premise:
(In certain experiments) genetic mutations occurred at random.
+
Choice (A):
All genetic mutations are random or no genetic mutations are random.
=
Conclusion:
All genetic mutations are random

Do you see how that conclusion results as an inference?

Suppose you give me a rule that says "All of Linda's friends are left-handed or none of Linda's friends are left-handed"

Now say we meet Roger, one of Linda's friends. If it turns out he's left-handed, then ALL of Linda's friends are left-handed. If it turns out he's not, then NONE of Linda's friends are left-handed.

That's how the Premise + Choice (A) ---proves--> Conclusion.

Don't worry that (A) is a CRAZY extreme idea. Sufficient Assumption is about thinking mathematically -- your job is just to find an answer choice that lets you PROVE (with no doubt whatsoever) that the conclusion is true.

Let me know if this doesn't make sense.

Although the Roger/Linda example is starting to make sense, I'm still a little confused about (A). I unfortunately crossed it off because I saw (A) as a restatement of the conclusion so I'm not sure how it can be an assumption as well.

[mirroredshades]

Although the Roger/Linda example is starting to make sense, I'm still a little confused about (A). I unfortunately crossed it off because I saw (A) as a restatement of the conclusion so I'm not sure how it can be an assumption as well.

The argument involves a noticeable scope shift (or two).

The experiment involves "certain kinds of" (or some) bacteria placed in a supply of nutrients, and it is discovered that the populations grew rapidly and that genetic mutations occurred at random in those populations.

The experimenter then concludes that all genetic mutations are random.

Notice the shift? It goes from "genetic mutations of certain bacteria are random" to "all genetic mutations are random".

Now, throw (A) into the mix. If some of the mutations were random, then all must be, because the other option is no longer viable. Either all are random or none are. Since in this experiment it was discovered that some types of bacteria have random genetic mutations, then with (A) we can conclude all are random.

(C) was the other answer choice I gravitated towards. But it is ultimately incorrect because the stimulus does not say that all bacteria undergo random genetic mutations. Only some types do. So the condition has not been met. (C) does not allow us to conclude anything; it does not allow us to bridge the gap between the evidence and the conclusion.

[WaltGrace1983]

This is a bit of a crazy question but let me see if my 2 cents offers anything to anyone.

In a particular (set of) experiment(s) with bacteria, genetic mutations occurred at random

-->

All genetic mutation is random

There is a giant hole here. Why? Because it goes from an observation from a particular experiment or a particular set of experiments (it doesn't really say which but that doesn't matter as much) to saying that what was observed is true for everything! It goes from talking about "certain kinds of bacteria" and the particular "genetic mutations" that occurred "at random" with them to ALL genetic mutations are random. Somebody never opened a Manhattan LSAT book . We are going to look for something that says that what is true for this experiment is true for everything - that the findings of this experiment as somehow or in some way representative of all genetic mutations.

(B) That's awesome but does it really matter if the bacteria is common or not? We are given bacteria in the argument so we don't need to dive any deeper into that idea. All we need to know is that the experiment showed something about this bacteria.

(C) This is definitely a big statement, which is good because our conclusion is a pretty big statement. It is saying that if all these mutations in bacteria are random, this is true for every other life form. Yet check this out (and if an instructor can chime on in my logic than I would greatly appreciate it). We are looking for something that is SUFFICIENT. We are looking for an answer choice that, if its true, will undoubtedly lead to the conclusion from the premise. Keep this in mind. Let's plug it in and see what happens.

In a particular (set of) experiment(s) with bacteria, genetic mutations occurred at random

+

If all genetic mutations are random, then all mutations in every other life are random too!

-->

All genetic mutation is random

Do you see the problem with this? We are assuming the conclusion to prove something about something else! THIS. IS. NOT. OUR. JOB. Our job is to understand why the premises do not justify to the conclusion and then plug in that hole! If we are just assuming that the conclusion is true (that all genetic mutations are random), we suck at our job! For sufficient assumption questions, don't assume the conclusion. Find the assumption that undoubtedly, 100%, non-negotiably, always, and ultimately leads to the conclusion. This answer choice does not do that and, thus, it shouldn't be tempting. Whenever you see IF + conclusion of the argument, be critical.

(D) I think this is the most tempting incorrect answer choice. It is saying that, regardless of the environment, we know that genetic mutation will occur in the same way. However, the problem with this is that we don't know anything about the environment of the experiments. In addition, how does this prove the conclusion? It doesn't. It is sometimes hard to eliminate these tempting, or perhaps even vague, answer choices in sufficient assumption questions. However, if it doesn't lead to the conclusion there isn't much you need to say otherwise. Just eliminate it.

(E) Nutrients? Nature? Where is the evidence about how this leads to something about "all" genetic mutation? This is vaguely incorrect answer choice but for the same reason as (D), we can eliminate it just because it doesn't lead to our conclusion.

(A) This one is great! If we prove something about ONE experiment involving genetic mutations, then we undoubtedly prove something about ALL genetic mutations. I like the example about friends and being left-handed above ^. I cannot explain it any more clearly than that.

[wxpttbh]

after viewing explanations above, I finally figure out why D choice is wrong. The implied words of D is to say, "All genetic mutations are random. " . Only with this implied condition, D makes sense.

[WendyQ765]

The conclusion is that the mutations of all life forms are random.
And the premise is the mutations of certain kinds of bacteria are random.
The gap here is how certain kinds of bacteria can show all life forms are same?

Answer choice A said all life forms are either random or not random. So if all are same, and one of them is random, then others are also random, because they are same. They just have two choice of mutation style and all of them must be same.

Answer choice C is wrong because it said if all bacteria are random, then all life forms are random. Yes, if we know all bacteria are random, it is right answer. But we only know certain kinds of bacteria are random. So it cannot get the conclusion.