nPr and nCr; what are they? How are they used in probability?

An explanation of why they work would be good too,

A link to somewhere for me to read for myself would be fine.

Question

nPr and nCr; what are they?  How are they used in probability?

An explanation of why they work would be good too,

A link to somewhere for me to read for myself would be fine.

anonymous · Answer

nCr is a formula that is used to SELECT r things out of n total ones. nPr is a formula that is used to ARRANge r things out of n totalones. A really good site tounderstand this : http://www.khanacademy.org/math/probability/v/permutations-and-combinations-1

anonymous · Answer

That's good @siddhantsharan 
It's called Permutations and Combinations.

anonymous · Answer

anonymous · Answer

in addition nCr is the number of combinations. nPr is the number of permutions.  both are basic in counting... without actually counting.

directrix · Answer

At the link, you will find some practice problems and answers. They are basic problems but will help you get the core concepts before moving to the difficult one. http://www.mytestbook.com/worksheet.aspx?test_id=1413&grade=7&subject=Math&topics=Permutations%20and%20Combinations