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In a class, each of the students were asked to pick an integ

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In a class, each of the students were asked to pick an integ [#permalink] New post 25 Dec 2012, 00:59
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In a class, each of the students were asked to pick an integer between 1 and 20, both inclusive. What is the probability that at least two students have picked up the same integer?

(1) There were less than 30 students.
(2) There were 30 students.

It's quite evident as to why
[Reveal] Spoiler:
(B)
is the answer here.
My question though is that is there anyway that we can solve this question?
I agree that it's a DS question but I couldn't help but wonder if there was a mathematical solution for this.

Cheers,
Taz
[Reveal] Spoiler: OA

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If this post helped you in your GMAT prep in anyway, please take a moment and hit the "Kudos" button.
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Re: Probability: students were asked to pick an integer between [#permalink] New post 25 Dec 2012, 03:01
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Expert's post
tabsang wrote:
In a class, each of the students were asked to pick an integer between 1 and 20, both inclusive. What is the probability that at least two students have picked up the same integer?

(1) There were less than 30 students.
(2) There were 30 students.


It's quite evident as to why
[Reveal] Spoiler:
(B)
is the answer here.
My question though is that is there anyway that we can solve this question?
I agree that it's a DS question but I couldn't help but wonder if there was a mathematical solution for this.

Cheers,
Taz


If there are more than 20 students then the probability is 100% that at least two students pick the same integer, which means that (2) is sufficient and (1) is not.

P.S. The question is flawed: on the GMAT, two data sufficiency statements always provide TRUE information and these statements never contradict each other.
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Re: Probability: students were asked to pick an integer between [#permalink] New post 25 Dec 2012, 04:43
Bunuel wrote:
tabsang wrote:
In a class, each of the students were asked to pick an integer between 1 and 20, both inclusive. What is the probability that at least two students have picked up the same integer?

(1) There were less than 30 students.
(2) There were 30 students.


It's quite evident as to why
[Reveal] Spoiler:
(B)
is the answer here.
My question though is that is there anyway that we can solve this question?
I agree that it's a DS question but I couldn't help but wonder if there was a mathematical solution for this.

Cheers,
Taz


If there are more than 20 students then the probability is 100% that at least two students pick the same integer, which means that (2) is sufficient and (1) is not.

P.S. The question is flawed: on the GMAT, two data sufficiency statements always provide TRUE information and these statements never contradict each other.



Thanks Bunuel. I too thought that there was something wrong about this question.
This is from a question set of a local GMAT tutorial.

Cheers,
Taz
_________________

If this post helped you in your GMAT prep in anyway, please take a moment and hit the "Kudos" button.
:) It'll make my day :)

Re: Probability: students were asked to pick an integer between   [#permalink] 25 Dec 2012, 04:43
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