Mathematics
OpenStudy (anonymous):

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.

OpenStudy (anonymous):

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

OpenStudy (anonymous):

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

OpenStudy (anonymous):
OpenStudy (anonymous):

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

Directrix (directrix):

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