Dear experts,

I am going through Permutation and Combinations chapter from Magical Boo on Quicker Maths by M. Tyra. I have stumbled on the following points:

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No. of selections of r things (r<=n) out of n identical things is 1

Total no. of selections of zero or more things from n identical thing = n+1

Total no. of selections of zero or more things from n different things = nC0 + nC1 + nC2 + nC3 +….nCn=(2)exp n

No. of ways to distribute (or divide) n identical things among r persons where any person may get any no of things = n+r-1Cr-1

Can anyone kindly refer me to a book on this subject or refer me to an article which can explain the above with an application or an example.

I am still in the process of going through this chapter for the second time, so most likely these are explained and I have not been able to associate these with the worked examples.

Kindly help

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