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QOTD: Many gardeners believe that the variety of clematis vine

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Re: QOTD: Many gardeners believe that the variety of clematis vine  [#permalink]

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New post 12 Apr 2018, 04:15
GMATNinja wrote:
The conclusion of this passage is that the gardener's belief--that jackmanii is the most popular variety of clematis vine among gardeners in North America (NA)--is apparently correct. The word "apparently" is very important here. The conclusion would be substantially different if we were to replace "apparently" with "definitely".

More on that in a moment... but first, why does the author conclude that the belief is apparently correct?

  • The largest clematis nursery in NA sells one million clematis plants per year.
  • Of the one million clematis plants sold per year by that nursery, ten percent are jackmanii.

A substantial chunk of the clematis plants sold at the largest nursery are jackmanii. The author reasons that jackmanii's popularity at the largest nursery is a good indicator of its popularity among NA gardeners.

But what about the other 90%? What if another variety of clematis accounts for MORE than 10% of the one million? In that case, jackmanii would not be the most popular variety at the nursery. However, if no other variety accounts for 10% (or more) of the one million, then jackmanii would be in fact be the most popular variety at the nursery.

Would that prove that jackmanii is the most popular variety in NA? Not necessarily. But if jackmanii is #1 at the largest nursery, that's certainly EVIDENCE that jackmanii is #1 in NA. Again, we are trying to conclude that the belief is APPARENTLY correct, not that the believe is DEFINITELY correct. As long as we have evidence that jackmanii is the most popular variety among NA gardeners, we're in good shape.

With that in mind, let's look at the answer choices:

Quote:
(A) The nursery sells more than 10 different varieties of clematis

If the nursery sells 10 varieties or fewer, then there would HAVE to be another variety that accounts for more than 10% of the one million plants sold at the nursery. If that were true, then jackmanii could not be the most popular variety at the nursery. Thus, we would not have evidence that jackmanii is #1 in NA. Without choice (A), the argument falls apart.

Now, does choice (A) PROVE that jackmanii is #1 at the nursery? Not at all... even with 20 varieties, there could be another type that accounts for more than 10% of the million. That, of course, would ruin the argument.

Even if choice (A) is true, the argument may or may not be valid, but that's okay. In other words, choice (A) doesn't PROVE that the author's reasoning is sound. But without choice (A), the author's argument could not be valid. This is a required assumption, so keep (A).

Quote:
(B) The largest clematis nursery in North America sells nothing but clematis plants

The nursery could sell many other types of plants. As long as jackmanii is the most popularity variety of clematis plant sold at the nursery, then the author's reasoning holds up. This is not a required assumption, so eliminate (B).

Quote:
(C) Some of the jackmanii sold by the nursery are sold to gardeners outside North America

If a substantial portion of jackmanii sales were to gardeners outside of NA, then we might have a problem. That might suggest that jackmanii's popularity at the nursery is NOT a good indicator of jackmanii's popularity among NA gardeners.

Choice (C) only says that SOME of the jackmanii are sold to gardeners outside of NA. In that case, the jackmanii sales at the nursery are probably a good indicator of its popularity among NA gardeners.

Does that make (C) a REQUIRED assumption? If (C) were not true and the nursery ONLY sold jackmanii to gardeners within NA, then that would probably further strengthen the argument. That would give us even more reason to believe that the sales at the nursery are a good indicator of NA popularity. Choice (C) is not a required assumption, so eliminate (C).

Quote:
(D) Most North American gardeners grow clematis in their gardens

It doesn't matter whether clematis is a popular plant in general. The belief is that jackmanii is the most popular variety OF clematis. Even if only a tiny fraction of NA gardeners grow clematis, jackmanii could still be the most popular variety among those gardeners who DO grow clematis. Eliminate (D).

Quote:
(E) For all nurseries in North America that specialize in clematis, at least 10% of the clematis plants they sell are jackmanii.

This is admittedly a little bit tempting: sure, it would strengthen the argument. But this isn't a strengthen question: we need to know whether this is NECESSARY to draw the conclusion.

And it isn't necessary: even if (E) is NOT true -- for example, if jackmanii accounts for less than 10% of clematis plants at a few nurseries -- it's still possible that jackmanii is the most popular. And since (E) isn't necessary, it's not the correct answer.

(A) is the best answer.


Even if A is not true the conclusion can be true. Consider a situation in which there are only two variety of clematis & the largest nursery export the other variety (which consists of 90%) to neighboring country and all of jackmanii's (10%) to NA still jackmanii's will be most popular, hence option A is not necessary for the conclusion to be true.
Please explain where I am making mistake?
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Re: QOTD: Many gardeners believe that the variety of clematis vine  [#permalink]

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New post 17 Apr 2018, 03:54
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All credits to CR Bible: This is an excerpt of my personal review session. Hope it helps:

First of all – before starting keep in mind that there are two types of assumptions: i) supporter assumptions and ii) defender assumptions. Let’ s provide an example of both:

i) Support assumption are assumptions that link together new elements in the stimulus or fill logical gaps in the argument. An example of this would be:

All male citizens of the Netherlands have the right to smoke weed. Therefore, Riccardo has the right to smoke weed in the Netherlands. The supporter assumption here is that Riccardo is a male citizen.

The fact that we assume Riccardo is a male citizen contains a piece of information not previously mentioned in the stimulus. In this case, Riccardo is a new element in the conclusion. This creates a gap in the conclusion. Therefore – the supporter assumption plays a paramount role in bringing these two terms together. Another example of this supporter assumption is:

All ducks in Martinique that have a really big beak are treated as holy and can therefore not be eaten by the local residents of Martinique. Therefore, Duckie, my favorite duck that I visit every day can’t be eaten by the local residents of Martinique.

The new element in the argument here is Duckie! The supporter assumption links this new piece of information together with the previous element. By assuming that Duckie has a really big beak.

ii) Defender assumptions are assumptions that contain statements that eliminate ideas or assertions that would undermine the conclusion. In some way, they defend the argument by showing that a possible source of attack is eliminated. Let’s take an example of this:

People who exercise a lot more perform better academically. Thus, exercising must cause a person to improve his/her grades. The author assumes here that the following assumptions aren’t true:

i) Sleeping more than eight hours a day doesn’t improve one’s grades.
ii) A high protein diet doesn’t enable someone to study more effectively and therefore improve their grades.

These hidden assumptions protect the argument against statements that would undermine the conclusion. Simply put, the author assumes that every alternate cause doesn’t exist!

Now let’s pivot back to the exercise at hand:

Many gardeners believe that the variety of clematis vine that is most popular among gardeners in North America is jackmanii. This belief is apparently correct since, of the one million clematis plants sold per year by the largest clematis nursery in North America, ten percent are jackmanii.
Which of the following is an assumption on which the argument depends?

(A) The nursery sells more than 10 different varieties of clematis
(B) The largest clematis nursery in North America sells nothing but clematis plants
(C) Some of the jackmanii sold by the nursery are sold to gardeners outside North America
(D) Most North American gardeners grow clematis in their gardens
(E) For all nurseries in North America that specialize in clematis, at least 10% of the clematis plants they sell are jackmanii.


Reviewing the stimulus we see:

Conclusion: The most popular variety clematis vine amongst gardeners in North America is jackmanii.

Premise: Of the one million clematis plants sold per year, by the largest clematis nursey in North America, ten percent are jackmanii.

Prephrase:
The new element in this stimulus here is the largest clematis nursery in North America. Remember that a supporter assumption brings together two pieces of new information. This would imply that the pieces sold at the largest clematis nursey are representative of the rest of the country. So we need a supporter assumption!

Let’s review the answer choices with this prephrase in mind:

a) The nursery sells more than 10 different varities of clematis. This would mean that the nursery indeed, is representative of the entire clematis vine population. If they would just sell two species, this would imply that that the jackmani is the least popular. This answer choise directly links the premise with the conclusion of the argument. CONTENDER!

b) Ok – if it only sells clematis plants that’s great for them. But does it really tell us anything about the variety of clematis vine? This answer choice is tricky, as it requires us to specifically understand what is being said. The word variety is key.

c) Some… This would merely imply that it is popular outside North America – but the conclusion focusses on inside North America. Out of scope.

d) Great for them – what is most? This would strengthen it in some way but is it the underlying assumption that holds the premise and conclusion together? No. Because if most NA gardeners grow it in this garden, this doesn’t tie together the element regarding the largest clematis nursery and the conclusion. Remember that this is an assumption question and not a strengthener.

e) This was my first answer choice – as it slightly matched my prephrase, but it’s wrong because: we still don’t know the amount of varieties each nursery holds. And therefore, doesn’t logically link the premise with the conclusion. Because it could still mean that the other nurseries sell only two/three varieties. Let’s label it as a contender for now.

Let’s use the assumption negation technique to decide between the two contenders. The assumption negation technique simply determines whether the negated answer choices weaken the argument, and therefore help identify the lynchpin of the argument - the assumption that holds the premise and conclusion together: the central nervous system, heart or brain whatever metaphor we want to use.

The assumption negation technique consists of two steps:

i) Logically negate the answer choices under consideration.
ii) The negated answer choice that attacks the argument will be the correct answer.
Understand that the consequence of negating an assumption is that the validity of the conclusion is called into question. So when we take away (negate it) the assumption – the building block of the argument – the entire reasoning structure is called into question.

Let’s negate:
a) The nursery doesn’t sell more than 10 different varieties of clematis.

b) For all nurseries in North America that specialize in clematis, at least 10% of the clematis plants they don’t sell are jackmanii. So 90% sold aren’t jackmani.

Which one of these weakens the argument?

If the nursery doesn’t sell more than 10 different varieties of clematies, this would mean that the 10% sold is actually less than the majority. If it sells 10 varieties for example, it is a mere 10% of the other varities, which would directly attack the premise and make weaken the argument the most. Therefore answer A is the right choice between A and E. For E – this would still mean that 10% sold are Jackmani and therefore doesn’t weaken the argument at all and is therefore not a supporter assumption that links the two pieces of information together.

So answer choice is A: for the simple fact that it’s a support assumption and when negated, the argument doesn’t hold, and we can therefore conclude that A is the entire lynchpin of the argument holding the premise and conclusion together.
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Re: QOTD: Many gardeners believe that the variety of clematis vine  [#permalink]

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New post 21 Apr 2018, 11:02
aditya201819 wrote:
Even if A is not true the conclusion can be true. Consider a situation in which there are only two variety of clematis & the largest nursery export the other variety (which consists of 90%) to neighboring country and all of jackmanii's (10%) to NA still jackmanii's will be most popular, hence option A is not necessary for the conclusion to be true.
Please explain where I am making mistake?

aditya201819, try reviewing these two posts:


Yes, even if there are fewer than ten varieties, jackmanii COULD still be the most popular in NA. And even if there are MORE than ten varieties, it might not be. But that's not the point. The question does NOT ask, "Which of the following must be true for jackmanii to be the most popular in NA?". The question asks, "Which of the following is an assumption on which THE AUTHOR'S LOGIC depends."

The author's conclusion is NOT: "Jackmanii is DEFINITELY the most popular in NA." The author's conclusion is that the belief is apparently correct. In other words, the author believes that the sales data from the nursery is EVIDENCE suggesting that the belief is true. Whether jackmanii is ACTUALLY the most popular is irrelevant.
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Re: QOTD: Many gardeners believe that the variety of clematis vine  [#permalink]

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New post 29 Aug 2018, 02:48
GMATNinja wrote:
The conclusion of this passage is that the gardener's belief--that jackmanii is the most popular variety of clematis vine among gardeners in North America (NA)--is apparently correct. The word "apparently" is very important here. The conclusion would be substantially different if we were to replace "apparently" with "definitely".

More on that in a moment... but first, why does the author conclude that the belief is apparently correct?

  • The largest clematis nursery in NA sells one million clematis plants per year.
  • Of the one million clematis plants sold per year by that nursery, ten percent are jackmanii.

A substantial chunk of the clematis plants sold at the largest nursery are jackmanii. The author reasons that jackmanii's popularity at the largest nursery is a good indicator of its popularity among NA gardeners.

But what about the other 90%? What if another variety of clematis accounts for MORE than 10% of the one million? In that case, jackmanii would not be the most popular variety at the nursery. However, if no other variety accounts for 10% (or more) of the one million, then jackmanii would be in fact be the most popular variety at the nursery.

Would that prove that jackmanii is the most popular variety in NA? Not necessarily. But if jackmanii is #1 at the largest nursery, that's certainly EVIDENCE that jackmanii is #1 in NA. Again, we are trying to conclude that the belief is APPARENTLY correct, not that the believe is DEFINITELY correct. As long as we have evidence that jackmanii is the most popular variety among NA gardeners, we're in good shape.

With that in mind, let's look at the answer choices:

Quote:
(A) The nursery sells more than 10 different varieties of clematis

If the nursery sells 10 varieties or fewer, then there would HAVE to be another variety that accounts for more than 10% of the one million plants sold at the nursery. If that were true, then jackmanii could not be the most popular variety at the nursery. Thus, we would not have evidence that jackmanii is #1 in NA. Without choice (A), the argument falls apart.

Now, does choice (A) PROVE that jackmanii is #1 at the nursery? Not at all... even with 20 varieties, there could be another type that accounts for more than 10% of the million. That, of course, would ruin the argument.

Even if choice (A) is true, the argument may or may not be valid, but that's okay. In other words, choice (A) doesn't PROVE that the author's reasoning is sound. But without choice (A), the author's argument could not be valid. This is a required assumption, so keep (A).

Quote:
(B) The largest clematis nursery in North America sells nothing but clematis plants

The nursery could sell many other types of plants. As long as jackmanii is the most popularity variety of clematis plant sold at the nursery, then the author's reasoning holds up. This is not a required assumption, so eliminate (B).

Quote:
(C) Some of the jackmanii sold by the nursery are sold to gardeners outside North America

If a substantial portion of jackmanii sales were to gardeners outside of NA, then we might have a problem. That might suggest that jackmanii's popularity at the nursery is NOT a good indicator of jackmanii's popularity among NA gardeners.

Choice (C) only says that SOME of the jackmanii are sold to gardeners outside of NA. In that case, the jackmanii sales at the nursery are probably a good indicator of its popularity among NA gardeners.

Does that make (C) a REQUIRED assumption? If (C) were not true and the nursery ONLY sold jackmanii to gardeners within NA, then that would probably further strengthen the argument. That would give us even more reason to believe that the sales at the nursery are a good indicator of NA popularity. Choice (C) is not a required assumption, so eliminate (C).

Quote:
(D) Most North American gardeners grow clematis in their gardens

It doesn't matter whether clematis is a popular plant in general. The belief is that jackmanii is the most popular variety OF clematis. Even if only a tiny fraction of NA gardeners grow clematis, jackmanii could still be the most popular variety among those gardeners who DO grow clematis. Eliminate (D).

Quote:
(E) For all nurseries in North America that specialize in clematis, at least 10% of the clematis plants they sell are jackmanii.

This is admittedly a little bit tempting: sure, it would strengthen the argument. But this isn't a strengthen question: we need to know whether this is NECESSARY to draw the conclusion.

And it isn't necessary: even if (E) is NOT true -- for example, if jackmanii accounts for less than 10% of clematis plants at a few nurseries -- it's still possible that jackmanii is the most popular. And since (E) isn't necessary, it's not the correct answer.

(A) is the best answer.


Just to add why E cannot be the answer!
The first part of the argument says " For all those specializing in Clematis ". So, there may or may not be other groups specializing in other plant varieties. In total it is impossible to tack on how other nurseries apart from " Clematis Specialists" will behave. Even if we negate the atleast 10% and get a range from 0% to less than 10%, we will end nowhere. Because the other nurseries can still make Jackmanii most popular.
Re: QOTD: Many gardeners believe that the variety of clematis vine &nbs [#permalink] 29 Aug 2018, 02:48

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