Hello, delso!

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 thatallgirls are adjacent.four

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.