Qualification > Math
Maths/Physics help
omarsubei:
Wow. I see. THhnk you very much
omarsubei:
I swear, if you solve this question, you're just a born genius! I've been trying it the whole day and I'm not getting the answer, which is 72.
I HATE Permutations and Combinations. Here it is:
"Mr Blue, Mr Black, Mr Green, Mrs White, Mrs Yellow and Mrs Red sit around a circular table for a meeting. Mr Black and Mrs White must not sit together.
Calculate the number of different ways these six people can sit at the table without Mr Black and Mrs White sitting together."
crucio:
u sure the ans is 72? im gettin 144...lol :D
astarmathsandphysics:
Soppose mr black site down fist then mrs white can site in one of 3 possible seats - draw it!. The other 4 guests can sit in 4! different ways with respect to oder. 3x24 =72
omarsubei:
--- Quote from: astarmathsandphysics on February 19, 2009, 12:59:31 pm ---Soppose mr black site down fist then mrs white can site in one of 3 possible seats - draw it!. The other 4 guests can sit in 4! different ways with respect to oder. 3x24 =72
--- End quote ---
Wait wait wait. I DID DRAW IT, a few million times too. Ya but what if Mr. Black changes his seat. He can also sit in six different places can't he. It's a permutation isn't it? Please explain more. There is actually a solution, but it's even more complex than yours:
"The number of different ways six people can sit around a circular table
is 5! = 120. (M1)
The number of different ways these six people can sit around a circular
table with Mr Black and Mrs White together is 4! × 2 = 48. (A1)
Therefore, the number of different ways these six people can sit around
a circular table with Mr Black and Mrs White NOT together is
120 – 48 = 72 "
Why can they sit in 5! ways, not 6! ???????
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