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.
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
That's good @siddhantsharan It's called Permutations and Combinations.
in addition nCr is the number of combinations. nPr is the number of permutions. both are basic in counting... without actually counting.
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
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