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n number of people are attending a meeting. All of them shake hands ea

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New post 03 Oct 2017, 01:38
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A
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C
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Difficulty:

  25% (medium)

Question Stats:

70% (00:37) correct 30% (00:49) wrong based on 30 sessions

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[GMAT math practice question]

n number of people are attending a meeting. All of them shake hands each other. If all attendees shake hands 210 times, what is the value of n?

A. 15
B. 19
C. 20
D. 21
E. 25
[Reveal] Spoiler: OA

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New post 03 Oct 2017, 01:40
MathRevolution wrote:
[GMAT math practice question]

n number of people are attending a meeting. All of them shake hands each other. If all attendees shake hands 210 times, what is the value of n?

A. 15
B. 19
C. 20
D. 21
E. 25


This is the same questions as the following one with one number different: https://gmatclub.com/forum/in-a-certain ... 47397.html
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New post 05 Oct 2017, 03:16
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nC2 = n(n-1)/2 = 210
n(n-1) = 420
n(n-1) – 420 = 0
n^2 – n – 420 = 0
(n-21)(n+20) = 0
n = 21 or n = -21
n = 21 since n must be positive.

Answer: D
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n number of people are attending a meeting. All of them shake hands ea   [#permalink] 05 Oct 2017, 03:16
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