perms and combs (1 Viewer)

[chowmeinbeanbo]

Hi guys,
for combs questions, I'm struggling to understand when you need to divide the whole thing by something factorial to get rid of 'order'. I get that you need to when there are equal groups, but I don't get why for picking cards out of a deck you don't need to divide. I have no idea when the order is introduced in my working out and when I need to account for it

Any help would be so appreciated!

 

[cossine]

When dealing with groups you are not going to care about order only what members a group consist of.

In the case of equal size group:

Let you say have a set of members L in group 1. and a set members K in group 2. It is also possible to have L in group 2 and K in group 1. Hence you divide.

but I don't get why for picking cards out of a deck you don't need to divide ? Dependent on what the question is asking.

Try to understand the binomial theorem. What is the importance of nCk in the bionomial theorem? How can this be generalised for multinominal theorem?

 

[chowmeinbeanbo]

Hi, thx for the reply.
I’m still confused though, is it ok if u give me an example for a pack of cards when u divide and when u do not?
That would be great

 

[cossine]

Hi, thx for the reply.
I’m still confused though, is it ok if u give me an example for a pack of cards when u divide and when u do not?
That would be great

When you want combination you need to divide by number of positions.

When you want permutation that is the number of arrangements you don't want to divide.

n-number of objects
r- number of objects selected

nPr is generally used for permutation.

nCr is generally used for combinations but can also be used for permutations. Why is it nCr can be used for permutations?

It not clear what you are asking. If you give an example I might be able to give better response.

 

[cossine]

Hi, thx for the reply.
I’m still confused though, is it ok if u give me an example for a pack of cards when u divide and when u do not?
That would be great

Assume cards of same character but different suit are different. That is club A, is different hearts A

How many combinations are there of 5 cards with characters A, K, J?

How many permutations are there of 5 cards with characters A, K, J?