Permuations/combination (1 Viewer)

[lyounamu]

http://www.boredofstudies.org/courses/maths/3u/2001_Maths3_T_CSSA_q.pdf

Page 2/6
Question 2C.

My working out is like the followings:

There are 5 ways in which vowels can be separated.
Those vowels can be arranged in 4!/2! ways
The non-vowels can be arranged in 5!/2! ways.

So I got: 5 . 4!/2! . 5!/2! = 3600

But mine is wrong. Can anyone explain?

 

[erm]

is answer 720?

 

[lyounamu]

is answer 720?

Yeah, it is.

 

[DownInFlames]

I think the method for this type of question is to figure out how many ways there are 2 or more vowels togther, then subtract this from the total number of possible arrangements.

Also don't forget about the 2 sets of repeat letters. (But I don't think you forgot in your method anyway)

 

[erm]

Well the way I saw it was that there were 5 consonants and 4 vowels.

EEIO (vowels) + XTNSN (consonants)

the line must look like this:

CVCVCVCVC

therefore
consonants can be arranged in 5!/2! ways
vowels can be arranged in 4!/2! ways

then (5!/2!)(4!/2!) = 720

 

[DownInFlames]

the line must look like this:

CVCVCVCVC

the line could also look like:

VCCVCVCVC

VCVCVCVCC

VCCVCVCCV

etc.


whatever it worked though.

 

[erm]

the line could also look like:

VCCVCVCVC

VCVCVCVCC

VCCVCVCCV

etc.


whatever it worked though.

yeah you're right. wtf am i thinking?

anybody tell me why i got it right?

 

[lyounamu]

the line could also look like:

VCCVCVCVC

VCVCVCVCC

VCCVCVCCV

etc.


whatever it worked though.

Yeah, that's how I found my answer because there are different ways in which vowels can consonants can be arranged. Damn, I don't know how to interpret quesiton. That will cost me heaps. :angry:

 

[DownInFlames]

Yeah, that's how I found my answer because there are different ways in which vowels can consonants can be arranged. Damn, I don't know how to interpret quesiton. That will cost me heaps. :angry:

Perms and Coms is shit hard in year 12. I reckon the questions are too fiddly for what they're worth.

But it will cost you 3 marks, or 3.5%. It's not that bad.

 

[lyounamu]

Perms and Coms is shit hard in year 12. I reckon the questions are too fiddly for what they're worth.

But it will cost you 3 marks, or 3.5%. It's not that bad.

Well, I guess I will still get 2/3 since my working out is decent. But I am worried that if I will get confused over this type of question in future. And I still don't understand how this is 720!!!

 

[DownInFlames]

Well, I guess I will still get 2/3 since my working out is decent. But I am worried that if I will get confused over this type of question in future. And I still don't understand how this is 720!!!

Can you ask your teacher next week? They should be able to help you, and maybe set you a few more questions for practise. I tried to work out the question but I haven't done perms and coms for that long that I can't quite get my head around it.

I do think the method we used for that type was to find the ways they would be together, and subtract this from the total.

 

[lyounamu]

Can you ask your teacher next week? They should be able to help you, and maybe set you a few more questions for practise.

Yeah, I will. Thanks for all the people who have contributed to this thread so far!

 

[erm]

yeah 720 would be correct if they said that the vowels and consonants alternate or something like that..

 

[erm]

lol shit, ive been calling them constants =_=

lawl

 

[lyounamu]

yeah 720 would be correct if they said that the vowels and consonants alternate or something like that..

No, they didn't Did they?

They never said they are alternate. They just said they are not grouped together.

 

[lolokay]

I would have just said: there's 5!/2 ways of arranging the consonants. There are now 6 places where vowels can go, and 2 of those places will not be filled - so you have 6!/2*2 ways of doing this *5!/2 = 10800

I know the question was incorrect, but would my working be correct?

 

[DownInFlames]

yeah, thats what she meant. the question should have said they alternated. the question was wording wrong so dont worry

But that would be too easy.

 

[DownInFlames]

this would still result in a number of cases

1) when all vowels are together
2) when 3 vowels are together
3) when 2 vowels are together, other 2 are seperated
4) when 2 pairs of vowels are together

theres no simple way to do the question properly. if the answers 720 the question should also state that the constants can not be together.

I think when you do the working for 2 vowels together, you should also get 4 vowels and 3 vowels together included in that, because one of the combinations of the remaining letters will include them being together with the others. It might work if you draw the little box pictures...

 

[erm]

But that would be too easy.

Well it's only in q 2 of the exam paper...