• Want to level up your HSC prep for Maths?
    Click here for details and register for the BoS Trials now!

Perms and Coms help please! (1 Viewer)

tracychau

New Member
Joined
May 27, 2015
Messages
14
Gender
Undisclosed
HSC
2017
"Eight children consisting of 3 boys and 5 girls are to be seated in a row. In how many ways can this be done if no boys are to be seated next to each other?"

The working out is 5! x 6P3 but I don't understand where the 6 comes from.
I'd gladly appreciate any help, thank you!
 

kawaiipotato

Well-Known Member
Joined
Apr 28, 2015
Messages
462
Gender
Undisclosed
HSC
2015
Set the girls first
So it looks like this: G G G G G
There are 6 possible spots for a boy to be seated such that a girl separates two boys (denoted by a star):
* G * G * G * G * G *
There are 6 spots possible for boy 1, 5 possible for boy 2, 4 for boy 3 = 6x5x4 = 6P3
Arranging the girls: 5!
So total = 6P3 x 5!
 

Users Who Are Viewing This Thread (Users: 0, Guests: 1)

Top