In a class, each of the students were asked to pick an integ : GMAT Data Sufficiency (DS)
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# In a class, each of the students were asked to pick an integ

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Intern
Joined: 14 Jun 2011
Posts: 17
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Kudos [?]: 48 [0], given: 24

In a class, each of the students were asked to pick an integ [#permalink]

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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)
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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Math Expert
Joined: 02 Sep 2009
Posts: 36567
Followers: 7081

Kudos [?]: 93224 [1] , given: 10553

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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)
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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Intern
Joined: 14 Jun 2011
Posts: 17
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Kudos [?]: 48 [0], given: 24

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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)
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.

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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