Subdivision of good cooks:
1) Gourmet cooks: Use extravagantly rich ingredients in elaborate recipes.
2) Fast food cooks: Use rich ingredients as longs as recipes are easy to follow and less time consuming.
3) Health food enthusiasts: Concerned with nutritional value.
All good cooks enjoy preparing and serving food, but they might not be big eaters.

(A) Most good cooks do not use extravagantly rich ingredients. If most good cooks might be of 2nd and 3rd type.
(B) Everyone who enjoys preparing and serving food is a good cook. All good cooks enjoy preparing and serving, but all who enjoy preparing and serving need not be good cooks.
(C) More good cooks who use extravagantly rich ingredients are big eaters than are good cooks who do not use such ingredients. If most good cooks are of the 1st type.
(D) There are fewer good cooks who enjoy serving and preparing food than there are good cooks who are big eaters. All good cooks enjoy preparing and serving (as mentioned), therefore, even if all are big eater as well, their no.s would be equal. It can never be possible that big eater> cooks who enjoy preparing and serving.
(E) Gourmet cooks, fast-food cooks, and cooks who are health food enthusiasts are all big eaters. Could be possible.

Although both 'B' and 'D' look incorrect, I would go still go with 'D' because that seems more improbable.

Please anybody, give a response which make 'B' or 'D', a better answer than the other.

Has to be D.

(A) Most good cooks do not use extravagantly rich ingredients. This could be true or false, the arguement doesn't mention any proportion of those that use rich ingredients, as to those that do not
(B) Everyone who enjoys preparing and serving food is a good cook. This could be true or false based on the paragraph. Of course in my own experience, this is false. Can't answer based on my own experiences
(C) More good cooks who use extravagantly rich ingredients are big eaters than are good cooks who do not use such ingredients. This could also be true or false. The arugumetn does not mention anything regarding proportion
(D) There are fewer good cooks who enjoy serving and preparing food than there are good cooks who are big eaters.ALL good cooks enjoy serving and preparing food, so it cannot be true that there are fewer of them than anything.
(E) Gourmet cooks, fast-food cooks, and cooks who are health food enthusiasts are all big eaters.Never addressed. Could be true or false

This question is on Extreme cases. IMO D is correct.

A) Most good cooks do not use extravagantly rich ingredients. [Can be true]
(B) Everyone who enjoys preparing and serving food is a good cook. [An extreme case but can be true]
(C) More good cooks who use extravagantly rich ingredients are big eaters than are good cooks who do not use such ingredients. [Can be true]
(D) There are fewer good cooks who enjoy serving and preparing food than there are good cooks who are big eaters. [Cannot be true as we are not given such facts in the stimulus]
(E) Gourmet cooks, fast-food cooks, and cooks who are health food enthusiasts are all big eaters. [Can be true]

my choice was E but after reading the explanation its D.

E was attractive because we need to look for the omission of the word 'GOOD'. If we miss that, we might chose the wrong answer.
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My answer is D

last premise states "But even though not all good cooks are big eaters, they all enjoy preparing and serving food".

Lets take example.... there are 100 good cooks

lets take big eaters be 70 as it is given that not all good cooks are big eaters.

All enjoy preparing and serving food so the number will be 100.


Now coming to option D it says

"There are fewer good cooks who enjoy serving and preparing food than there are good cooks who are big eaters".

Obviously not possible due to reasons mentioned above.

Hope this helps...!!!

We know that "not all good cooks are big eaters", or in other words, that 'some good cooks are not big eaters'. E is tempting if you assume that the stem gives an exhaustive list of the types of good cooks, but there's no reason to think that the classification of cooks in the stem is comprehensive. There might be a fourth category of good cook that is never mentioned in the passage: It may be, say, that some good cooks are 'decorative cooks' who only enjoy cooking because they like arranging food artistically on a plate. Further, it may be that these 'decorative cooks' are the only cooks who are not big eaters, while all other cooks are big eaters. So E can be true.

D cannot possibly be true. We're told in the stem that all good cooks enjoy serving food, while not all are big eaters, so the number who enjoy serving food is greater than the number who are big eaters.
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Okay,
It's been a long time no one posted a response to the question.
I just tried the question today and here is what I think about it

Lets say All good cooks = Gourmet cooks + Fast-food cooks + Health food cooks + OTHER Good cooks
(A) Most good cooks do not use extravagantly rich ingredients. => Gourmet cooks are not most of the lot. Argument does not say anything about Gourmet cooks proportion in the total cook population. So their population could be 80%(in that case it is the most = So CAN BE TRUE) or may be 10% (in that case it would be least=So CAN'T BE TRUE).
(B)Everyone who enjoys preparing and serving food is a good cook. => It is talking about the population as a whole and we do not know any of it.So CAN BE OR CAN'T BE TRUE
(C)More good cooks who use extravagantly rich ingredients are big eaters than are good cooks who do not use such ingredients. =>Again we do not know anything about the proportion of cooks with in COOK POPULATION .So we can not compare them. they could certainly be true. OR could certainly not be true.
(D)There are fewer good cooks who enjoy serving and preparing food than there are good cooks who are big eaters. =>
Well here we go . We do not know about the individual cook population type .But from the last line of the argument "But even though not all good cooks are big eaters, they all enjoy preparing and serving food." => THEY ALL = All good cooks = Gourmet cooks + Fast-food cooks + Health food cooks + OTHER Good cooks
AND This number i.e. THEY ALL > BIG EATER COOKS
And the Option says just the opposite i.e. THEY ALL < BIG EATER COOKS
AND That for 100% CAN NOT BE TRUE
(E) We do not need to think about This option as we have got our answer
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Although I know OA is D, I am still confused between B and D.

D is clearly incorrect.
But I am not able to categorize B under could be true or must be true. And thus feel B is also incorrect.

Stimulus states, If somebody is a good cook --> He/She will enjoy preparing and serving the food.
Thus, contrapositive would be, If He/she doesn't enjoy preparing and serving the food --> He/she is not a good cook [Reverse+Negation]

B option states, Everyone who enjoys preparing and serving the food --> is a good cook [case of Mistaken Reversal]
and Hence this cannot be true.

Please let me know the genuine reason for rejecting B.

Option B MUST not be true or false, but it CAN be true or false - the questions asks which one MUST be false.

IF the set of good cook and the set of people who enjoy preparing and serving food are identical, THEN option B is true. Thus option B can be true under certain condition. Hence it cannot be the right answer, because the right answer CANNOT be true under any condition.

I got this answer right, and was able to analyse thoroughly and comprehensively, and I could answer this with confidence. But my concern is on the timing. Though I get most of the medium-hard level question right (accuracy of ~80-85%), I take too long to get to these answers (approx. 4 to 5 minutes). I know I am quite in the early stages of my preparation(roughly 3rd week in CR), how do I improve the timing on questions? Is it ok the way I am progressing or should do something consciously to get my timing on questions better. Any help would be much appreciated.