A group consisting of N couples are going to see a movie. : GMAT Data Sufficiency (DS)
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# A group consisting of N couples are going to see a movie.

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22 Mar 2011, 19:50
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A group consisting of N couples are going to see a movie. The seats in each row of the theater is greater than 2N. If the group decides to all sit in the same row, each couple is indifferent to empty seats next to them, and each couple insists on sitting together, how many seating arrangements are possible?

(1) N = 5

(2) The group will all sit next to one another, starting with the first seat in the row.
[Reveal] Spoiler: OA

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Re: A group consisting of N couples are going to see a movie. [#permalink]

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22 Mar 2011, 20:18
First I thought s1 is sufficient but on taking a closer look the statement said greater than 2N seats. Hence C is sufficient. You have only three answers- a,c or worst case e. If this question turns out to be your 31-37 question take a moment to think why answer may not be E.

If the seats would have been Exactly 2N the answer is A. Please correct if the reasoning has flaw

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22 Mar 2011, 20:32
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Seats in each row greater than 2N brings possibility to increase no be seats in a row up to 100 to 1000 to millions. However N could be 2, 4 , 6.
There could be 1 or 50 or 100 or .. seats gap between each couple.Any number of arrangement is possible.
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22 Mar 2011, 20:46
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gmat1220 wrote:
First I thought s1 is sufficient but on taking a closer look the statement said greater than 2N seats. Hence C is sufficient. You have only three answers- a,c or worst case e. If this question turns out to be your 31-37 question take a moment to think why answer may not be E.

If the seats would have been Exactly 2N the answer is A. Please correct if the reasoning has flaw

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You are right; if the seats were exactly 2N, the arrangements would be = 5!*(2)^5 and "A" would have sufficed. St2 tells us that they are all seating together without any gaps starting with the FIRST seat, which now means that they are indeed occupying first 10 seats of the row and the rest of the seats become immaterial and makes "C" sufficient.

Ans: "C"
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22 Mar 2011, 21:59
@bhandariavi: Can you tell me the source of this question???
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22 Mar 2011, 22:09
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@fluke - "if the seats were exactly 2N, the arrangements would be = 5!*(2)^5 "

Is it something like - 5 couples in 5 pairs of seats = 5!

and then 2 persons in each of the 5 couples can be arranged among themselves as 2!

So total 5! * (2!)^5

= 5! * (2)^5
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Re: A group consisting of N couples are going to see a movie. [#permalink]

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22 Mar 2011, 22:37
subhashghosh wrote:
@fluke - "if the seats were exactly 2N, the arrangements would be = 5!*(2)^5 "

Is it something like - 5 couples in 5 pairs of seats = 5!

and then 2 persons in each of the 5 couples can be arranged among themselves as 2!

So total 5! * (2!)^5

= 5! * (2)^5

Precisely!!!

If you adhere all the couples and make them one unit each; there are 5 units;

5 units can be arranged in 5! ways

And within the unit; every couple can rearrange in 2! ways.
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15 Apr 2013, 06:29

If the seats are more than 2N, there is no upper limit.

So, if we use the counting principle, depending on the value of 2N, the number of options available to the first couple could be 100, 1000 or whatever. SUbesquent couples would be limited by where the first couple chose to sit.

In this case, shouldn.t the answer be E?
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Re: A group consisting of N couples are going to see a movie. [#permalink]

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15 Apr 2013, 06:37
12bhang wrote:

If the seats are more than 2N, there is no upper limit.

So, if we use the counting principle, depending on the value of 2N, the number of options available to the first couple could be 100, 1000 or whatever. SUbesquent couples would be limited by where the first couple chose to sit.

In this case, shouldn.t the answer be E?

Take a closer look at the second statement: The group will all sit next to one another, starting with the first seat in the row.
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01 Oct 2014, 01:46
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Re: A group consisting of N couples are going to see a movie. [#permalink]

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29 Oct 2014, 08:39
Bunuel wrote:
12bhang wrote:

If the seats are more than 2N, there is no upper limit.

So, if we use the counting principle, depending on the value of 2N, the number of options available to the first couple could be 100, 1000 or whatever. SUbesquent couples would be limited by where the first couple chose to sit.

In this case, shouldn.t the answer be E?

Take a closer look at the second statement: The group will all sit next to one another, starting with the first seat in the row.

Hi

Can you please explain me meaning of "each couple is indifferent to empty seats next to them"?
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09 Jan 2016, 06:18
Hello from the GMAT Club BumpBot!

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A group consisting of N couples are going to see a movie. [#permalink]

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23 Feb 2016, 18:07
bhandariavi wrote:
A group consisting of N couples are going to see a movie. The seats in each row of the theater is greater than 2N. If the group decides to all sit in the same row, each couple is indifferent to empty seats next to them, and each couple insists on sitting together, how many seating arrangements are possible?

(1) N = 5

(2) The group will all sit next to one another, starting with the first seat in the row.

1 alone is insufficient..the 5 couples can be arranged in 5!*2!^5 ways (2! because the 2 from the couples can be arranged in 2! ways, and ^5 because 5 pairs). but we are told that there are >2N seats..so this makes us additional problems..what if there are 11 seats? then the total number of ways would be 11!/5!2!...so different numbers...

2 says that the couple will sit starting the first seat from the row..meaning that if there are 11 seats, and there are 5 couples, the couples will sit in the first 10...so the last one is irrelevant, and does not need to be taken into account. this alone is insufficient.

1+2 -> we know that there are 5 couples, and that they will take the first seats in the row..so no additional possibilities...total 5!*2!^2
A group consisting of N couples are going to see a movie.   [#permalink] 23 Feb 2016, 18:07
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