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December 06, 2021, 01:51:09 pm

### AuthorTopic: Combinations and Permutations for Unit 3 & 4?  (Read 533 times)

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#### GreenNinja

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##### Combinations and Permutations for Unit 3 & 4?
« on: October 23, 2021, 02:45:17 pm »
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Hi,

I am doing QCE Methods U3 and 4 now. Started this term. To prepare for the upcoming year I went to the Unit 1 and 2 content to make sure I know everything very well.

So.. I finished this 'revision' a week ago. I can fluently complete nearly all questions from all chapters except "Combinations" and "Permutations"

I have spent ages trying to understand this topic well, but some complex unfamilier and oddly written complex familiar questions still trip me up. Sometimes the wording and how we are soppoused to answer.

I have looked at the unit 3 and 4 syllubus. In unit 3 is all about derivatives, however in unit 4. continous random variables, distribution, sample proportion and confidence intervals pop up.

A friend told me that nCr is used in these. However, I would like to know is nPr and nCr are needed. And for the ones that are neessecary for Unit 3 and 4, what kind of questions are likely to pop up (wordy questions where we find the possible arrangments with restrains such as 'containing two vowels and two different consonants)

Thanks alot!!

#### RuiAce

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##### Re: Combinations and Permutations for Unit 3 & 4?
« Reply #1 on: October 23, 2021, 05:27:18 pm »
+1
I had a look in your QCE syllabuses. Did you mean to post this here? It looks like combinatorics belongs to specialist maths, not methods. The only thing I see in methods is use of nCr for the binomial expansion, and subsequently understanding the binomial distribution. Both of which, luckily don't require deep combinatorial thinking.

Combinatorics can be a hard topic though, mainly because the way of thinking is often different to everything else in high school math. More can be discussed in the specialist forum.

#### GreenNinja

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##### Re: Combinations and Permutations for Unit 3 & 4?
« Reply #2 on: October 23, 2021, 05:55:57 pm »
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Did you mean to post this here? It looks like combinatorics belongs to specialist maths, not methods. The only thing I see in methods is use of nCr for the binomial expansion, and subsequently understanding the binomial distribution. Both of which, luckily don't require deep combinatorial thinking.

Hi RuiAce,

In both the cambridge and jacaranda U1&2 books, there is a large portion of questions on these topics. I was unable to get my head fully round it, so thats why I was confused. I have checked the syllabus again, you are right it is only nCr they explicitly mention that we need to learn, however it does menation counting patters, and the textbooks do include both topics (there are more formulas the textbook uses as well).

BTW, if anyone knows if counting methods are used in things like sample proportion, please tell me.

Anyway, thanks for you help!

« Last Edit: October 23, 2021, 05:57:49 pm by Tech1234 »

#### RuiAce

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##### Re: Combinations and Permutations for Unit 3 & 4?
« Reply #3 on: October 23, 2021, 06:45:11 pm »
+3
Hi RuiAce,

In both the cambridge and jacaranda U1&2 books, there is a large portion of questions on these topics. I was unable to get my head fully round it, so thats why I was confused. I have checked the syllabus again, you are right it is only nCr they explicitly mention that we need to learn, however it does menation counting patters, and the textbooks do include both topics (there are more formulas the textbook uses as well).

BTW, if anyone knows if counting methods are used in things like sample proportion, please tell me.

Anyway, thanks for you help!

It does appear that there is a "Counting and probability" topic in the Unit 2 syllabus. But it doesn't look like a combinatorics chapter. Rather, it looks like a chapter on fundamental concepts in probability (e.g. mutually exclusive events, conditional probability). Although there may be some "counting" required, they should not be using the fancier counting techniques, as you would otherwise see in specialist.

If you want to post one or two specific questions (from either textbook) for some example guidance, that's up to you. If I find I had to use combinatorics concepts solving them, I'd be quite concerned. (Unless of course, the textbooks gave a disclaimer that there's some specialist coverage.) But some less advanced concepts in "counting" seem justified.

(Also, it would be weird if counting patterns were a part of sample proportions. One of them is a more probability focused concept, whilst the other is a statistics focused concept (which happens to build upon the binomial distribution somehow).)