pclawong wrote:
chetan2u wrote:
hazelnut wrote:
If 6 people are going to sitting at a round table, but Sam will not sit next to Suzie, how many different ways can the group of 6 sit?
(A) 120
(B) 108
(C) 96
(D) 74
(E) 56
Hi...
6 people can be arranged in (6-1)!=120ways
Now let sam and Suzie be sitting together and hence there are 5 people
Ways = (5-1)!*2=4!*2=48.... Multiplication by 2 is cater for sam-suzane and suzane-sam..
Ways they don't sit together=120-48=72..
hazelnut, D may be 72 and not 74..
Dear,
I don't understand why it is 5! way to seat 6 people.
and I don't get how do you get 48 way for not siting together
Sorry, I really wanna know
Hi
pclawongi think i can help you with this.
first of all if 6 people are sitting around a table, and the condition is Sam will not sit next to Suzie.
this will be equal to
total no. of ways 6 people can sit around a table - total no of ways in which Sam will always sit next to Suzienow total no of ways, 6 people can sit around a circular table is (6-1)!
and total no of ways, Sam will always sit next to Suzie is (5-1)! 2!
Note: total no. of ways in which n different things can be arranged around a circular path is (n-1)! now let me tell you why we are doing (5-1)! 2! for the later case-
in later case we are assuming that Sam will always sit next to Suzie, so we are considering them as a single unit saying that now we have 5 people not 6.
now number of way, 5 people can sit around a circular table is (5-1)!
now again Sam & Suzie can interchange their position so we are doing 2! for them
so now total no. of ways, Sam will always sit next to Suzie is (5-1)! 2!
now the question is asking about ways in which Sam will not sit next to Suzie.
we subtract (5-1)! 2! into total no of ways which is (6-1)!
(6-1)! - (5-1)! 2!
hope this will help you.