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Seated next to eachother

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Re: Seated next to eachother

by logitech » Thu Nov 20, 2008 1:57 pm
Carloblacksun wrote:In many ways can Ann, Bea, Cam, Don, Ella, and Fay be seated if Ann and Bea cannot be seated next to each other?

a) 240
b) 360
c) 480
d) 600
e) 720
Bonjour Paris,

What you want to do is:

1) Find the possible seatings - without any restriction

A B C D E F = 6!

2) Have A & B sit next to each other and GLUE them together so they act like a Siamese twin :)

AB C D E F = 5!

and remember they can also switch places - :!:

BA C D E F = 5 !

3) Not If you subtract what you have just found from the all possible ways:

6! - 2 x 5 ! = 5! ( 6 - 2 ) = 120 x 4 = 480
LGTCH
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by earth@work » Thu Nov 20, 2008 2:07 pm
same as logitech:
total ways = 6!
ways when Ann & bea always together = 5! *2 (consider Ann bea as one object and they themselves can be seated in 2 ways, therefore 5! multiplied by 2)
difference = when ann & bea never together = 5!(6-2)=480
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by Carloblacksun » Thu Nov 20, 2008 2:17 pm
thanks a lot guys! I am quite quick in calculation so it took 4/5 minutes to make the ABCDEF count, but this formula is much quicker...

would you consider this question EXTREMELY difficult or not so much?
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by logitech » Thu Nov 20, 2008 2:22 pm
Carloblacksun wrote:thanks a lot guys! I am quite quick in calculation so it took 4/5 minutes to make the ABCDEF count, but this formula is much quicker...

would you consider this question EXTREMELY difficult or not so much?
I hate to say this but it is very basic question for its types. This shit can get really ugly.
LGTCH
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