Permutation and Combination - Number of selection of r things

Dear experts,

Can you please refer me to any online material/book which will demonstrate the application of the below rule with examples.
Please help.

Rule:Number of selection of r things (r<=n) out of n identical things is 1


Thank you
ExcellearnerAsked:
Who is Participating?

[Product update] Infrastructure Analysis Tool is now available with Business Accounts.Learn More

x
I wear a lot of hats...

"The solutions and answers provided on Experts Exchange have been extremely helpful to me over the last few years. I wear a lot of hats - Developer, Database Administrator, Help Desk, etc., so I know a lot of things but not a lot about one thing. Experts Exchange gives me answers from people who do know a lot about one thing, in a easy to use platform." -Todd S.

ste5anSenior DeveloperCommented:
Huh? When you have a bag of n identical marbles, how many different ways do you have to draw two marbels?

Combination: Order or sequence does not matter.
Permutation: Order or sequence does matter.

For example:
Bag (n=3) of (Red, Red, Red)
The only possible result for drawing two marbles is: Red, Red. Cause there is no other combination or permutation.
All combination and permutation problems are normally reduced to sets. Thus each element is different from each other.

Bag (n=3) of (Red, Blue, Green)
Possible draws of two: RB, BG, RG ( and BR, GB, GR) => 3 combinations or 6 permutations

The only problems arise in mix forms

Bag (n=3) of (Red, Blue, Blue)
Possible draws of two: RB, RB, BB ( and BR, BR)  => 2 combinations or 3 permutations.
0

Experts Exchange Solution brought to you by

Your issues matter to us.

Facing a tech roadblock? Get the help and guidance you need from experienced professionals who care. Ask your question anytime, anywhere, with no hassle.

Start your 7-day free trial
aburrCommented:
"Rule: Number of selection of r things (r<=n) out of n identical things is 1"
-
the Number of selection of r things (r<=n) out of n identical things is 1 only if r = n.
The fact the all n are identical can cause trouble with interpretation.
ste5an addresses this problem correctly
0
It's more than this solution.Get answers and train to solve all your tech problems - anytime, anywhere.Try it for free Edge Out The Competitionfor your dream job with proven skills and certifications.Get started today Stand Outas the employee with proven skills.Start learning today for free Move Your Career Forwardwith certification training in the latest technologies.Start your trial today
Math / Science

From novice to tech pro — start learning today.