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Carla is having a dinner party and is inviting 5 guests, 3 [#permalink]
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19 Sep 2005, 14:51
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This topic is locked. If you want to discuss this question please repost it in the respective forum. 9. Carla is having a dinner party and is inviting 5 guests, 3 boys and 2 girls. Carla knows that she needs to sit at the head of the table, but hasnâ€™t decided on fixed seats for anyone else. If she decides not to sit any of her guests next to anyone else of the same gender, how many different seating arrangements are possible?
1. 6
2. 12
3. 24
4. 60
5. 120



VP
Joined: 22 Aug 2005
Posts: 1112
Location: CA

2. 12
Carla sits at fixed position.
3 boys
2 gals
in order not to sit two persons with same gender together,
1 gal need to sit between 2 boys.
3 boys themselves can be rearranges in 3! = 6 ways
the two inbetween positions can be filled by 2 gals in 2! = 2 ways
total arrangements: 6 * 2 = 12



Senior Manager
Joined: 15 Aug 2005
Posts: 257
Location: Las Vegas, NV

I got 24.
three seats across from two seats with Carla at the head of the table.
The order of the three seats has to be BGB: so, 3*2*2
On the two seat side it can either be BG or GB, so 2 ways there
3*2*2*2=24



VP
Joined: 22 Aug 2005
Posts: 1112
Location: CA

popew626 wrote: I got 24.
three seats across from two seats with Carla at the head of the table.
The order of the three seats has to be BGB: so, 3*2*2
On the two seat side it can either be BG or GB, so 2 ways there
3*2*2*2=24
are we considering table as Rectangular? My explanation assumes dinner table to be circular.



Senior Manager
Joined: 15 Aug 2005
Posts: 257
Location: Las Vegas, NV

I don't think it's circular because there is no "head" of the table with a circular table. Plus, wouldn't the question say that the table is circular since the formula is different for circular combos? I admit that the question needs further definition.



Intern
Joined: 19 Aug 2005
Posts: 41

Even when the table is rectangular, i get 12
carla at the head of the table
2 boys sit beside her chair
2 girls sit on the chairs next to the boys
and finally one guy sits on the other head chair
this way no person of same sex sitting beside each other
so we get 3! arrangements for boys and 2! arrangments for girls
total 12



Senior Manager
Joined: 04 May 2005
Posts: 279
Location: CA, USA

i also got 12
Carla is not to sit with a girl herself, I assume



Senior Manager
Joined: 29 Nov 2004
Posts: 483
Location: Chicago

i get 12...carla is not inculded in the deal
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Manager
Joined: 26 Jun 2005
Posts: 122

I got 12...I assumed that Carla is not included in the calculation as well.
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Intern
Joined: 02 Sep 2005
Posts: 17

The OA is B (12).
Moving clockwise around the table, Carla is at the head of the table and we know that seat 1 must be occupied by a boy, and there are 3 different boys who could fill this spot. Seat 2 must then be a girl. There are 2 different girls who could fill this spot. Seat 3 is another boy. Now that one of the boys is seated (next to Carla), only 2 boys remain for this seat. Seat 4 is a girl, and only one girl remains to sit here. Finally, only one boy remains for seat 5 next to Carla. So we have 3x2x2x1x1 = 12



VP
Joined: 22 Aug 2005
Posts: 1112
Location: CA

acid_burn wrote: The OA is B (12).
Moving clockwise around the table, Carla is at the head of the table and we know that seat 1 must be occupied by a boy, and there are 3 different boys who could fill this spot. Seat 2 must then be a girl. There are 2 different girls who could fill this spot. Seat 3 is another boy. Now that one of the boys is seated (next to Carla), only 2 boys remain for this seat. Seat 4 is a girl, and only one girl remains to sit here. Finally, only one boy remains for seat 5 next to Carla. So we have 3x2x2x1x1 = 12
Although I assumed while solving this question, how do we know if the table is round or rectangular..what is head of the table in circular table? does ans differ?



Manager
Joined: 06 Aug 2005
Posts: 197

I think that what is meant by this question is a rectangular table.
Head of table at one end, two seats on either side of that end, one seat at opposite end to head of table. No difference between this mathematically and a circular table with one fixed seat.
In a circular arrangement, head of table is defined as wherever the head of the table wants to sit !



Senior Manager
Joined: 15 Aug 2005
Posts: 257
Location: Las Vegas, NV

Yeah, the question should definitely say what shape the table is.










