In the jar there are white and black marbles (W>0 and B>0). : GMAT Data Sufficiency (DS)
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# In the jar there are white and black marbles (W>0 and B>0).

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In the jar there are white and black marbles (W>0 and B>0). [#permalink]

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09 Oct 2009, 14:08
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In the jar there are white and black marbles (W>0 and B>0). How many black marbles are there?

(1) There are total 101 marbles in the jar.
(2) From any two marbles from the jar at least one is white.
[Reveal] Spoiler: OA

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09 Oct 2009, 14:36
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Bunuel wrote:
Try this one from me.

In the jar there are white and black marbles (W>0 and B>0). How many black marbles are there?

(1) There are total 101 marbles in the jar.
(2) From any two marbles from the jar at least one is white.

Explanation of the answer to follow.

C. If white marbles were 100 and 1 Black marble, then only you get at least 1/2 while drawing 2 marbles from the jar. But you do not get answer (no. of black and white marbles) until you mix 1 and 2.
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09 Oct 2009, 14:50
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GMAT TIGER wrote:
Bunuel wrote:
Try this one from me.

In the jar there are white and black marbles (W>0 and B>0). How many black marbles are there?

(1) There are total 101 marbles in the jar.
(2) From any two marbles from the jar at least one is white.

Explanation of the answer to follow.

C. If white marbles were 100 and 1 Black marble, then only you get at least 1/2 while drawing 2 marbles from the jar. But you do not get answer (no. of black and white marbles) until you mix 1 and 2.

Maybe you misunderstood the statements, or I stated them ambiguously
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09 Oct 2009, 22:58
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Bunuel wrote:
GMAT TIGER wrote:
Bunuel wrote:
Try this one from me.

In the jar there are white and black marbles (W>0 and B>0). How many black marbles are there?

(1) There are total 101 marbles in the jar.
(2) From any two marbles from the jar at least one is white.

Explanation of the answer to follow.

C. If white marbles were 100 and 1 Black marble, then only you get at least 1/2 while drawing 2 marbles from the jar. But you do not get answer (no. of black and white marbles) until you mix 1 and 2.

Maybe you misunderstood the statements, or I stated them ambiguously

I guess I overlooked - thought white for black. It is B.
Given that: w>0 and b>0.

(1) Total = 101 tells nothing about individusl msrbles.
(2) If any two marbles from the jar are drawn, at least one is a white. That means black cannot be more than 1. so Black = 1 irrespective of whites.

Another good one. Are you gmat instructer/question writer?
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09 Oct 2009, 23:21
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Yes you're right. Answer B. +1.

Thats what I like in this problem: the number of black marbles are in no connection with total number of marbles. Simple logic.

I'm neither gmat instructor nor question writer, I'm just preparing for GMAT. Just found that composing questions helps me to understand better the logic of the quant problems in GMAT.
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10 Oct 2009, 02:59
Awesome question.. I arrived at E.
Line of reasoning: At least one white means that number of white > 50% of total...however even after combining we cannot tell the exact number of whites..it can be 60%(Total) or 70%(Total)..

The catch is the word "any" in B. If ANY two marbles are picked and if black can be 1(max) means, there is only one black !!!!
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10 Oct 2009, 08:10
Economist wrote:
Awesome question.. I arrived at E.
Line of reasoning: At least one white means that number of white > 50% of total...however even after combining we cannot tell the exact number of whites..it can be 60%(Total) or 70%(Total)..

The catch is the word "any" in B. If ANY two marbles are picked and if black can be 1(max) means, there is only one black !!!!

Thanks Economist, I knew that this trap ("any" in second statement) would work.

And yes answer is 1 black marble, (2) alone is sufficient. B.
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10 Oct 2009, 08:30
I guess thats the best way to practice gmat.

Your questions are perfectly up to the real gmat standard.

lol................ +1

Bunuel wrote:
Yes you're right. Answer B. +1.

Thats what I like in this problem: the number of black marbles are in no connection with total number of marbles. Simple logic.

I'm neither gmat instructor nor question writer, I'm just preparing for GMAT. Just found that composing questions helps me to understand better the logic of the quant problems in GMAT.

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05 Jan 2010, 12:24
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Bunuel wrote:
Yes you're right. Answer B. +1.
I'm neither gmat instructor nor question writer, I'm just preparing for GMAT. Just found that composing questions helps me to understand better the logic of the quant problems in GMAT.

Awesome question.....! U preparing for GMAT! U mite end up getting 900 score in it :D LOL!!
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Re: In the jar there are white and black marbles (W>0 and B>0). [#permalink]

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19 Jan 2014, 05:32
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Re: In the jar there are white and black marbles (W>0 and B>0). [#permalink]

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06 Feb 2014, 23:43
Goodday Bunuel
Can you please explain why it is B??...
Option B says : "From any two marbles from the jar at least one is white"...This means 1 or both are white but the question asks "how many?"....I am stuck here
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Re: In the jar there are white and black marbles (W>0 and B>0). [#permalink]

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25 Feb 2014, 10:18
If there were 2 black balls, there is a chance of picking up two black balls.
But the second statement states that from any two marbles from the jar AT LEAST 1 is white meaning there is only 1 black ball in the jar.

srinjoy28 wrote:
Goodday Bunuel
Can you please explain why it is B??...
Option B says : "From any two marbles from the jar at least one is white"...This means 1 or both are white but the question asks "how many?"....I am stuck here
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Re: In the jar there are white and black marbles (W>0 and B>0). [#permalink]

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25 Feb 2014, 10:50
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Bunuel wrote:
In the jar there are white and black marbles (W>0 and B>0). How many black marbles are there?

(1) There are total 101 marbles in the jar.
(2) From any two marbles from the jar at least one is white.

My take is B.

consider 1 alone) it tells us nothing about the number of white or black marbles in particular.

consider 2 alone) consider the total number of marbles to be 5 (for simplicity, it can be extended up to infinite number of marbles)
let the 5 marbles be --> A,B,C,D and E.
now option 2 says, if we pick any 2 marbles...at least 1 of them would be white.
if we form every possible group of 2 from these, we get - AB,AC,AD,AE,BC,BD,BE,CD,CE and DE. (10 groups, which is nothing but C(5,2))
since at least one of any two is white, we can safely say A,B,C and D are definitely white. E can be either black or white. but since our fact statement says W>0 and B>0; E has to be a black marble.
Hence, with statement 2 alone we can determine the number of black marbles...which would always be 1.

Good question.
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26 Apr 2015, 22:36
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Bunuel you were preparing for GMAT!!!!!!(P.S i just came to know that) sorry mate but there is no school for you not atleast on this planet my advice is please look in some other galaxy. For god's sake please tell me who can teach bunuel anything hahahaha. now i know from where the real competition comes in this exam. envy you bunuel
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Re: In the jar there are white and black marbles (W>0 and B>0). [#permalink]

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08 Sep 2015, 19:53
ahhh!!! This was tricky!!!
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Re: In the jar there are white and black marbles (W>0 and B>0). [#permalink]

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10 Sep 2015, 02:35
My GMAT is after a day. Any prior notes to study that is important??
Re: In the jar there are white and black marbles (W>0 and B>0).   [#permalink] 10 Sep 2015, 02:35
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