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In a group, what percentage of members speak both french and English?

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In a group, what percentage of members speak both french and English? [#permalink]

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New post 21 Nov 2017, 20:22
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In a group, what percentage of members speak both french and English?

(1) 50% members speak English
(2) 80% members speak French
[Reveal] Spoiler: OA

Kudos [?]: 14 [0], given: 129

Manager
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Joined: 24 Jun 2017
Posts: 119

Kudos [?]: 14 [0], given: 129

Re: In a group, what percentage of members speak both french and English [#permalink]

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New post 21 Nov 2017, 20:27
Hi Guys
today I bumped into the following DS question (source Experts Global)
How do you think, does the answer fully correspond and respect GMAT DS logic?
I personally found it super confusing

Answer explanation
[Reveal] Spoiler:
Answer E, both statements are not sufficient. As we don't know how many members don't speak either of 2 languages so we can't determine

Kudos [?]: 14 [0], given: 129

Expert Post
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V
Joined: 02 Sep 2009
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Re: In a group, what percentage of members speak both french and English? [#permalink]

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New post 21 Nov 2017, 20:30
cbh wrote:
In a group, what percentage of members speak both french and English?

(1) 50% members speak English
(2) 80% members speak French


General formula for two groups;
{Total} = {Group 1} + {Group 1} - {Both} + {Neither}

100 = 50 + 80 - {Both} + {Neither}

As, you can see without knowing {Neither} group we cannot answer the question.

Answer: E.

19. Overlapping Sets



Hope it helps.
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Kudos [?]: 14 [0], given: 129

Re: In a group, what percentage of members speak both french and English? [#permalink]

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New post 21 Nov 2017, 20:43
Bunuel wrote:
As, you can see without knowing {Neither} group we cannot answer the question.

Answer: E.
Hope it helps.


Thanks Bunuel for replying
I've already checked all those links and both formulas and I feel pretty confident with set questions.
So I can assume if I deal with DS set questions on test day, the question should always precise if there is someone in {Neither} group OR answer is E, right?
I was almost sure that GMAT doesn't trick candidates in that way...

Kudos [?]: 14 [0], given: 129

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Re: In a group, what percentage of members speak both french and English? [#permalink]

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New post 21 Nov 2017, 20:46
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Expert's post
cbh wrote:
Bunuel wrote:
As, you can see without knowing {Neither} group we cannot answer the question.

Answer: E.
Hope it helps.


Thanks Bunuel for replying
I've already checked all those links and both formulas and I feel pretty confident with set questions.
So I can assume if I deal with DS set questions on test day, the question should always precise if there is someone in {Neither} group OR answer is E, right?
I was almost sure that GMAT doesn't trick candidates in that way...


I wouldn't call this a trick. This is natural and logical: of course there could be a group which does not speak any of the two languages, why not? Thinking otherwise would be assumption.
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Please read this: Ultimate GMAT Quantitative Megathread | All You Need for Quant | PLEASE READ AND FOLLOW: 12 Rules for Posting!!!

Resources:
GMAT Math Book | Triangles | Polygons | Coordinate Geometry | Factorials | Circles | Number Theory | Remainders; 8. Overlapping Sets | PDF of Math Book; 10. Remainders | GMAT Prep Software Analysis | SEVEN SAMURAI OF 2012 (BEST DISCUSSIONS) | Tricky questions from previous years.

Collection of Questions:
PS: 1. Tough and Tricky questions; 2. Hard questions; 3. Hard questions part 2; 4. Standard deviation; 5. Tough Problem Solving Questions With Solutions; 6. Probability and Combinations Questions With Solutions; 7 Tough and tricky exponents and roots questions; 8 12 Easy Pieces (or not?); 9 Bakers' Dozen; 10 Algebra set. ,11 Mixed Questions, 12 Fresh Meat

DS: 1. DS tough questions; 2. DS tough questions part 2; 3. DS tough questions part 3; 4. DS Standard deviation; 5. Inequalities; 6. 700+ GMAT Data Sufficiency Questions With Explanations; 7 Tough and tricky exponents and roots questions; 8 The Discreet Charm of the DS; 9 Devil's Dozen!!!; 10 Number Properties set., 11 New DS set.


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Re: In a group, what percentage of members speak both french and English? [#permalink]

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New post 21 Nov 2017, 20:48
Since Bunnel has posted there is no point in posting again but still this is my take
statement 1
insufficient . we don't know the percentage of french
statement 2
We don't know the percentage of English
insufficient
combine statement 1 and statement 2
when we have overlapping sets , it is necessary to know the condition if anything satisfies both the individual statements or if it satisfies neither .
Here 2 cases could be possible :
1. members who speak English also speak french or vice versa ( how will we know the information from given statements- insufficient)
2. members neither speaking English or french (we don't know about it either. hence insufficient)

hence the answer is E

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In a group, what percentage of members speak both french and English? [#permalink]

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New post 21 Nov 2017, 21:02
Bunuel wrote:
I wouldn't call this a trick. This is natural and logical: of course there could be a group which does not speak any of the two languages, why not? Thinking otherwise would be assumption.

awesome thanks. I got confused because I thought that in terms of GMAT, the "overlapping" nature of sets - it's an additional condition, that should be clarified in the question and if not shouldn't be taken into account. I mean, I can develop this logic further, we don't know if any member speaks any language but english and french. I mean that kind of problem is not an algebraic expression or calculus or geometry where you have clear although wide framework to operate within it and you don't have to make any assumptions that contradict that framework.
i will try to cover more set questions to catch on

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In a group, what percentage of members speak both french and English?   [#permalink] 21 Nov 2017, 21:02
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