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A group consists of a few men and a few women. What is the total numbe

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New post 16 Jul 2017, 23:34
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A group consists of a few men and a few women. What is the total number of men and women in the group?


(1) The ratio of the number of ways in which the people in the group are seated along a circle so that men and women sit in alternate positions and the number of ways in which the people in the group are seated in a row so that men and women sit in alternate positions is 1 : 10.

(2) The number of handshakes possible separately among the men and separately among the women is equal and each is equal to 5/12 of the number of handshakes possible if the men and women shake hands only with each other such that every man shakes hands with every woman.

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Re: A group consists of a few men and a few women. What is the total numbe  [#permalink]

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New post 19 Jul 2017, 06:04
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Bunuel wrote:
A group consists of a few men and a few women. What is the total number of men and women in the group?


(1) The ratio of the number of ways in which the people in the group are seated along a circle so that men and women sit in alternate positions and the number of ways in which the people in the group are seated in a row so that men and women sit in alternate positions is 1 : 10.

(2) The number of handshakes possible separately among the men and separately among the women is equal and each is equal to 5/12 of the number of handshakes possible if the men and women shake hands only with each other such that every man shakes hands with every woman.


Answer is (D).

1) When men and women have to sit in alternate positions along a circle, the number of men has to be equal to the number of women.
Let number of men = x.
Therefore, the number of women is also x.

(x!).(x!) / (x!).(x+1).(x!) = 1/10.

Solving the above equation, we get x=9.
Therefore total number of people =2x = 18.

2) Let total number of men = x and total number of women =y.

xC2 = yC2 = (5/12)(x.y)

Solving, we get x=y=6.
Therefore, total number of people are 12.

Hence answer is (D).
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Re: A group consists of a few men and a few women. What is the total numbe  [#permalink]

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New post 16 Aug 2017, 04:46
Is this some sort off formulae for the formation.?
(x!).(x!) / (x!).(x+1).(x!) = 1/10.

Also, can someone explain how to solve the 2nd statement.?
From Shariq41's explanation, how can 2 statements come with 2 different answers.?

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A group consists of a few men and a few women. What is the total numbe  [#permalink]

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New post 16 Aug 2017, 10:44
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shariq41 wrote:
Bunuel wrote:
A group consists of a few men and a few women. What is the total number of men and women in the group?


(1) The ratio of the number of ways in which the people in the group are seated along a circle so that men and women sit in alternate positions and the number of ways in which the people in the group are seated in a row so that men and women sit in alternate positions is 1 : 10.

(2) The number of handshakes possible separately among the men and separately among the women is equal and each is equal to 5/12 of the number of handshakes possible if the men and women shake hands only with each other such that every man shakes hands with every woman.


Answer is (D).

1) When men and women have to sit in alternate positions along a circle, the number of men has to be equal to the number of women.
Let number of men = x.
Therefore, the number of women is also x.

(x!).(x!) / (x!).(x+1).(x!) = 1/10.

Solving the above equation, we get x=9.
Therefore total number of people =2x = 18.

2) Let total number of men = x and total number of women =y.

xC2 = yC2 = (5/12)(x.y)

Solving, we get x=y=6.
Therefore, total number of people are 12.

Hence answer is (D).


Hi Bunuel
Can you provide the official explanation or point out if there are any errors in my approach because this is a weird question as getting two different answers from each statement which is not possible in a DS question

Statement 1: In a circular arrangement if men & women are sitting in alternate position, then number of men and women have to be equal.
let the number of men = women = \(n\)
\(n\) people can be arranged in a circular table in \((n-1)!\) ways and for the remaining \(n\) people there are \(n\) spaces available now. so the remaining \(n\) people can be arranged in \(n\)! ways.
Thus total number of ways of arranging men and women in a circular table, alternately \(= (n-1)!*n!\)

In a linear arrangement if we start with men and then alternately arrange men and women, then the number of ways will be \(= n!*n!\)
but we can also start with women, hence total number of ways of linearly arranging men & women alternatively \(= 2*n!*n!\)

As per statement \(\frac{(n-1)!*n!}{2*n!*n!}\) = \(\frac{1}{10}\)
Solving the equation we get \(n = 5\). Hence the statement is sufficient

Statement 2: Clearly states that number of handshakes are equal, hence number of men = number of women = \(n\)
Number of handshakes among each men or women themselves \(= n_C_2\)
Total number of handshakes between \(n\) men & \(n\) women \(= n*n = n^2\)
as per the statement \(n_C_2\) = \(\frac{5}{12}*n^2\)
Solving the equation we get \(n = 6\). Hence Sufficient.

Option D
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A group consists of a few men and a few women. What is the total numbe  [#permalink]

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New post 16 Aug 2017, 16:59
sarugiri wrote:
Is this some sort off formulae for the formation.?
(x!).(x!) / (x!).(x+1).(x!) = 1/10.

Also, can someone explain how to solve the 2nd statement.?
From Shariq41's explanation, how can 2 statements come with 2 different answers.?


About solution of statement 2:

The total number of handshakes (each man with each woman) = n*n=sqr(n)
When men shake hands with each other, the number of handshakes for first man = n-1
for the second - n-2
...
for the last - 0.
It is arithmetic progression, sum it up.
n-1 + n-2 + ... + 0 = ((n-1 + 0)/2)*n
So ((n-1 + 0)/2)*n = 5/12*n*n --->n = 6.

I would like to know too about different answers.
But I suppose, we put in statement 1 not 1/10, but 1/12, and everything will be ok
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Re: A group consists of a few men and a few women. What is the total numbe  [#permalink]

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New post 16 Aug 2017, 18:33
Bunuel,
please provide a solution for this :(
thank you very very much
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Re: A group consists of a few men and a few women. What is the total numbe  [#permalink]

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New post 16 Aug 2017, 18:40
What is statement 2 actually mean? Can anyone translate it for me,

if the men and women shake hands only with each other such that every man shakes hands with every woman, each is equal to 5/12 of the number of handshakes possible , <<what is that mean? What is the 5/12 stand for?

Thank you so much
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Re: A group consists of a few men and a few women. What is the total numbe  [#permalink]

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New post 16 Aug 2017, 22:44
pclawong wrote:
What is statement 2 actually mean? Can anyone translate it for me,

if the men and women shake hands only with each other such that every man shakes hands with every woman, each is equal to 5/12 of the number of handshakes possible , <<what is that mean? What is the 5/12 stand for?

Thank you so much


Hi pclawong

Statement 2 implies that if men shake hands among themselves or if women shake hands among themselves, then that number will \(\frac{5}{12}\) \(of\) the number of handshakes if every men shakes hands with every women.

So for example if the number of handshakes among men themselves is \(x\)
and the number of handshakes among men and women = \(y\)
then \(x= \frac{5}{12}*y\)

--== Message from the GMAT Club Team ==--

THERE IS LIKELY A BETTER DISCUSSION OF THIS EXACT QUESTION.
This discussion does not meet community quality standards. It has been retired.


If you would like to discuss this question please re-post it in the respective forum. Thank you!

To review the GMAT Club's Forums Posting Guidelines, please follow these links: Quantitative | Verbal Please note - we may remove posts that do not follow our posting guidelines. Thank you.
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Re: A group consists of a few men and a few women. What is the total numbe   [#permalink] 16 Aug 2017, 22:44
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