Q21 - Consumer Magazine: Because front-loading washers...

[smiller]

Question Type:
Necessary Assumption

Stimulus Breakdown:
Premise:
ordinary powder detergent does not dissolve readily in front-loading washers

Conclusion:
to get clothes really clean, front-loading washers must use special detergent instead of ordinary detergent

Answer Anticipation:
For the conclusion to be guaranteed, it's necessary to assume that if detergent does not dissolve readily in in a washer, the clothes will not get really clean.

Correct Answer:
(D)

Answer Choice Analysis:
(A) This is out of scope. The stimulus mentions the amount of water that each type of washer uses, but this essentially functions as background information. The conclusion isn't based on the amount of water, but rather on the fact that ordinary detergent doesn't dissolve readily in front-loaders.

(B) This is also out of scope, although it looks tempting! We do have to make an assumption about detergent formulated for front-loading washers compared to ordinary powder detergent. Specifically, we have to assume that the former dissolves more readily in front-loading washers than the latter does. However, this answer choice isn't comparing the two types of detergent. Choice (B) is about how well detergent for front-loading washers dissolves in top-loading washers. We don't care about that.

(C) This also looks tempting at first, but it's too broad. "A washing machine" in choice (C) means "all washing machines." What happens if (C) isn't true? What if some washing machines are able to get clothes really clean using ordinary powder detergent? Maybe top-loaders can do this. If that's the case, it might still be true that front-loaders need special detergent. In other words, the argument could still be valid even if choice (C) is false, so choice (C) is not an assumption that the argument requires.

(D) This is correct. It is the assumption we anticipated, and is required for the argument to hold: if a detergent does not dissolve readily, it does not get clothes really clean.

(E) This is out of scope. Like (A), this involves the amount of water used by a washer, which isn't the real basis for the argument. Choice (E) doesn't tell us anything about the need to use special detergents in front-loaders.

Takeaway/Pattern: Necessary Assumption questions often have tempting answer choices that seem relevant, but are not actually necessary. The argument holds up just fine if the answer choice isn't true. If you have a free Manhattan Prep account, you can download our "Negate These" flashcard set and improve your ability to spot answers that are tempting, but not actually necessary.

#officialexplanation

[emilyrcicero]

Hey Guys -- I got this one wrong initially and thought I'd share my review in case anyone else got stuck too. I make no guarantees as to accuracy but this is the method (of madness) I used to find correct answer...

C: to get clothes really clean in front-load you need to use detergent formulated especially for front-load machines instead of ordinary power detergent
Why?
P1: front-load uses less water than top-load therefore power detergent doesn't dissolve readily
I identified/pre-phrased 2 gaps:
-Detergent formulated for front-load dissolves readily
-Dissolving readily is required for getting clothes really clean

First time around, I went with answer choice C because I was focusing on the phrase "to get clothes really clean" but when I went back and reviewed I realized D was the correct answer as it basically restates (but in the negative) one of the gaps I identified (dissolving readily key to really clean clothes).

Hope this helps!

[rinagoldfield]

Great explanation, emilycicero!

[sumukh09]

D is also a sufficient assumption. Just wanted to add that!

[jan]

can someone explain why C would be wrong though?
The conditional logic would be established as :

Really clean → laundry detergent specially formulated

And although I understand that D points out the gap that dissolution is a prerequisite, I don't see how it establishes the first part of the conclusion, that a detergent formulated especially for front-loading washers NEED to be used.
IMO, it seems like I need to make an additional assumption that specially formulated detergent is the only one that dissolves well.

What am I doing wrong?

[pewals13]

(C) is wrong because you don't HAVE to assume that for any washing machine to get clothes really clean that a special detergent must be used- this only needs to be true for front loaders in order for the conclusion to have any chance at being true

[tennisboy12]

When you see answer choice (D), with the unless statement, how are you supposed to negate it? "A laundry detergent does get clothes really clean in a washer "without"(?) it dissolving readily in it. Thank you very much.

[daijob]

Why is E incorrect? In the premise says it uses less water, so I thought that's the problem...is it wrong because it is a premise to support the intermediate conclusion "ordinary powder detergent does not dissolve readily"?

[christine.defenbaugh]

Thanks for posting, daijob!

If the argument requires an assumption to get from the premise to the intermediary conclusion, that assumption would be a perfectly valid answer choice! Unfortunately, that's not what (E) is doing here.

Let's take a look at JUST what you are calling the premise-IC core. (I'm not 100% convinced this IS a premise-IC core, but for argument's sake, let's take a look.)

PREMISE: Front-loaders use less water than top-loaders
INTER. CONCLUSION: ordinary powder detergent doesn't dissolve readily in front-loaders

If this is an argument core, then I absolutely need the 'less water' distinction to be somehow relevant to the detergent not dissolving. However, I don't need that relationship to be true for all washers, of every time, everywhere... I only need it to be true insofar as it applies to front-loaders and top-loaders. (E) goes way too far - it's giving us a comparative relationship for all washers!

I actually think that the entire first sentence is just premise (all facts), here. The word "because" CAN signal premise, but it can also signal a causation relationship between two facts. If I say "Mary is tired this morning because she stayed out all night", that may not be an argument - I may be telling you two facts: Mary is tired, and Mary stayed out all night AND I'm telling you there's a causal relationship between the two.

What do you think?

[shirleyx]

for my own sake, maybe for yours as well..

NECESSARY ASSUMPTION

[to get really clean clothes with FLM, you need special detergent for FLM instead of ordinary powder detergent]
because...
-ordinary powder detergent does not readily dissolve in FLM

Flaw: .... something missing about readily dissolving and having clean clothes

(A) who cares about TLM
(B)who cares about TLM
(C)unsupported, i don't know if ONLY special detergents clean in a washing machine -- I'm interested only with FLM. this is too general of a statement to be a necessary condition for my argument
(D) adresses the two missing links I was suspicious about.. leave for now
(E) Who cares about water usage

confirming the correct answer

negation of (D) says that a detergent does not have to readily dissolve to really clean... well, in this case, i no longer need special detergent for FLM... thus, this is a necessary assumption to reach the conclusion of the argument.

[maria487]

The most tempting answer choices were B-D. I was able to eliminate B and C, and thereby arrive at D.

Core: Powder detergent doesn't dissolve readily in front loading washers --> Need to use a specially formulated FL detergent rather than powder detergent in FL machines to get clothes really clean.

B is wrong because it is comparing laundry detergent dissolving in front loading vs top loading washers. We don't care if one laundry detergent dissolves more readily in front loading or top loading. I think this AC would be correct if it instead said "a laundry detergent formulated for FL washers dissolves more readily in them than does ordinary powder detergent." Remember that that is what we are comparing, not the rate of dissolving of any given detergent in FL vs TL.

C is not necessary. We know that for a FL machine we need a specially formulated detergent. But this does not mean that specially formulated detergent is necessary for any washing machine.

D is correct! Look at the term mismatch between the premise and conclusion. The premise talks about detergent dissolving and the conclusion talks about a detergent that is made for FL washers that is not ordinary powder detergent. The assumption is that ~dissolve readily --> ~get clothes really clean. To get clothes really clean, the detergent must dissolve readily.

[contropositive]

When you see answer choice (D), with the unless statement, how are you supposed to negate it? "A laundry detergent does get clothes really clean in a washer "without"(?) it dissolving readily in it. Thank you very much.

Buy the Manhatten LR 4th edition if you haven't already, which goes over these rules.

For unless statements, the part after unless is negated and the other part is the sufficient.

D would read, "if it DOES NOT dissolve readily in it, then a laundry detergent does not get clothes really clean"


if you look at the argument that is exactly what it is assuming: if it doesn't dissolve readily in FL washers, then does not get cloth really clean

Side Note: If an original argument included the word "unless" and it followed a component logic then the answer choice would negate the component (and vs or).

[hwangbo.edu]

D is also a sufficient assumption. Just wanted to add that!

While I initially viewed Answer D as a SA, after closer scrutiny I think otherwise:

Argument Core:
P: O --> not DR (contrapositive: DR --> not O)
C: RC --> not O --> S

Answer D:
RC-->DR

O (Ordinary detergent in front-loader)
DR (Dissolves Readily in front-loader)
RC (Really Clean in front-loader)
S (Special detergent in front-loader)

The conclusion introduces two new elements (RC & S) but only RC is linked to the premise, by Answer D (RC --> DR --> not O). The link to S (not O --> S)remains an unsupported gap:

This means another NA could be, for example, "There is no additive to ordinary detergent that would cause it to dissolve readily in a front-loader." Negated, this would lead the argument to another conclusion (i.e., ordinary detergent, in lieu of special detergent, can really clean clothes in a front-loader).

Because Answer D does not completely bridge the gap between the premise and conclusion, it's not an actual SA but rather (correctly) a NA. Well played, LSAC, well played.

[ManhattanPrepLSAT1]

Solid work hwangbo!

[hayleychen12]

I got this one right during my timed exam.

But looking back to it, I have a problem.

Premise: Ordinary detergent (OD) does not dissolve readily in front-loading washers.

Conclusion: To get clothes clean, we need to use a special detergent.

(D) says If a detergent get clothes clean, it dissolves readily.

But do we really need to assume D?

May be the special detergent still cannot dissolve readily, but it has other content that can get the clothes clean.

I think for D to be an accurately right answer, the last sentence of the stimulus need to be like" ......you need to use a detergent formulated especially for front-loading washer which can dissolves readily , instead of ordinary powder detergent."

[hnadgauda]

core: ordinary powder detergent doesn't dissolve readily in front-loading washers because the washers use less water --> you need to use a detergent formulated especially for front-loading washers to get clothes really clean in a front-loading machine

Gap: detergents formulated especially for front-loading washers dissolve readily in front-loading machines (or in less water); to get clothes really clean in a front-loading machine, they must be washed by a detergent that dissolves readily in front-loading machines

A: No; our argument is about front-loading machines; top-loading machines don't matter
B: Negation: laundry detergent formulated for front-loading washers does NOT dissolve more readily in these washers than in does in top-loading washers; this doesn't destroy our argument. Using this special detergent can still make our clothes really clean in FL washers.
C: Negation: If washing machines don't get clothes really clean, then they must be using a laundry detergent specially formulated for that machine.
D: Negation: a laundry detergent gets clothes clean in a washer unless it dissolves readily in it.
E: Same as A; eliminate because we are talking about machines that use LESS water.

It looks to me that the negations of both C and D destroy the argument. Can you please check if I negated the answers correctly and why C's negation doesn't destroy the argument?

[ohthatpatrick]

The negations for (C) and (D) are not correct.

When you negate a conditional, you don't get a conditional.


I could say
"If you're a girl, you love Justin Bieber"
(that's equivalent to "All girls love Justin Bieber")

When we negate something, we're just prefacing it with
IT IS FALSE TO SAY THAT ...

If I say
IT IS FALSE TO SAY THAT "All girls love justin bieber",
I'm not committing myself to a conditional idea.

I'm just saying "Some girls might not love justin bieber". That's enough to contradict the original claim.

For (C), it's "not ONLY with specially formulated detergent .... You can get clothes really clean with a non-specially formulated detergent too."

For (D), it's "You don't HAVE to have the detergent dissolve readily in order to get really clean clothes ... You can get clothes really clean even if the detergent doesn't dissolve readily".

[can_I_ever_reach_a_170?]

Hello!
Can I ask a quick structure-related question?

I find the whole first sentence as Premise, and the next second setence as Main Conclusion.
But can I say the Premise in this stimulus has a Premise and a Subsidiary Conclusion components in it?
Sometimes, the Method question asks a part within the whole sentence. So I’m just curious.

[ohthatpatrick]

If you see the structure:

Because claim 1, claim 2. So, claim 3

you could definitely say
claim 1 - premise
claim 2 - intermediate conclusion
claim 3 - main conclusion

However, you sometimes want to differentiate between causal uses of words like thus/therefore/because/since and argument uses of those words.

CAUSAL USES
He jumped off a ten story building. Thus, he died.
Because he jumped off a ten story building, he died.

ARGUMENT USES
He jumped off a ten story building. Thus, he must have wanted to commit suicide.
Since he jumped off a ten story building, he must have wanted to commit suicide.

In the first sentence here, the REASONING CORE (if there is one) would be
IF uses less water, THEN dissolves less readily.

I'm tempted to see that more as cause/effect than as premise/conclusion. But you're not going crazy to think that the structural placement of words is setting up

BECAUSE [premise], [intermediate conclusion]. SO [main conclusion]

[ZarkaS555]

I thought there were two assumptions at play here: 1: that in order the get things really clean, the detergent would have to dissolve readily and 2: that a detergent specially formulated for a front loading washing machine will dissolve readily. I'm confused by how answer choice D fills those gaps. Even if a laundry detergent needs to dissolve readily to get clothes really clean, we still don't know whether the specially formulated detergent does dissolve readily.

So confused