Perms (1 Viewer)

[moderntortoisecat]

Find the number of different ways in which n students can stand in a row when two are boys, the rest are girls and the boys all stand together

Five drummers and five singers sit together in a row. In how many ways can this be done if a particular drummer must not sit between two particular singers?

 

[WeiWeiMan]

Find the number of different ways in which n students can stand in a row when two are boys, the rest are girls and the boys all stand together

Five drummers and five singers sit together in a row. In how many ways can this be done if a particular drummer must not sit between two particular singers?

1)
(n-2) girls and 2 boys
Treat the two boys as one 'entity' and hence arrange (n-1) entities. Then, arrange the two boys.
i.e. possible permutations = 2! * (n-1)!

2)
5 drummers, 5 singers, 10 total people
the total number of ways to arrange these people in a line is 10!
the number of ways in which the conditions are met is the total number of ways - the number of the in which the condition is NOT met.

there are 2 IMPORTANT singers and 1 IMPORTANT drummer, hence 10-2-1 =7 other people
treat these 3 IMPORTANT people as 1 entity that can be arrange in two ways (the drummer must stay in the middle),

hence ways = 10!-8! * 2 = 3548160


note: if it's wrong don't blame me plz

 

[Susu123]

1)
(n-2) girls and 2 boys
Treat the two boys as one 'entity' and hence arrange (n-1) entities. Then, arrange the two boys.
i.e. possible permutations = 2! * (n-1)!

2)
5 drummers, 5 singers, 10 total people
the total number of ways to arrange these people in a line is 10!
the number of ways in which the conditions are met is the total number of ways - the number of the in which the condition is NOT met.

there are 2 IMPORTANT singers and 1 IMPORTANT drummer, hence 10-2-1 =7 other people
treat these 3 IMPORTANT people as 1 entity that can be arrange in two ways (the drummer must stay in the middle),

hence ways = 10!-8! * 2 = 3548160


note: if it's wrong don't blame me plz

is this stuff in yr 12 as well? or just prelims?

 

[WeiWeiMan]

is this stuff in yr 12 as well? or just prelims?

Prelim course but it is assessed in HSC

 

[Susu123]

Prelim course but it is assessed in HSC

oop i guess i gotta revise them then, thanks

 

[Average Boreduser]

oop i guess i gotta revise them then, thanks

 

[WeiWeiMan]

oop i guess i gotta revise them then, thanks

prelim content is like 30-40% of the hsc iirc

 

[Susu123]

prelim content is like 30-40% of the hsc iirc

oh damn I didn't know that
but then again a lot of the stuff im doing rn i feel like i did last year, so makes sense

 

[Average Boreduser]

oh damn I didn't know that
but then again a lot of the stuff im doing rn i feel like i did last year, so makes sense

 

[Susu123]

why u mad at me

 

[Average Boreduser]

why u mad at me

BECAUSE I CAN

 

[Susu123]

BECAUSE I CAN

OK