Correct!Ten Students sit in a row.
Find the probability of 6 boys and 4 girls can be arranged if
(i) all girls are side by side?
My working: .
(ii) all girls are seperated by boys.
Why cant i just take 10! - 120,960=3,507,840? .This is wrong!
The ans given is: 604,800.
You subtracted the number of ways that all four girls are adjacent.
What about "3 adjacent girls" or "2 adjacent girls"?
Here is how I handle "not adjacent" problems.
Place the 6 boys in a row.
Insert a space before, after and between them.
. . .
There are permutations of the boys.
Choose 3 of the 7 spaces and assign the girls.
There are choices.
Therefore, there are: . ways.