Question

In how many ways can 7 people be seated in a row of chairs if two of the people, Wilma and Paul, refuse to sit next to each other

Answer 1

Answer:

let X be the number of ways they can be seated without condition,

let M the the number of ways they can be seated if the two people must sit together,

let N be the number of ways they can be seated if the two must not sit together.

X=7! =5040

M= 6!× 2!=1440

M+N=X

then N=X–M=5040–1440=3600ways