+23246 nPr represents permutations and its formula is: nPr = n! / (n - r)!
Permutations find the number of possibilities when order is important.
When order is not important, use combinations.
nCr represents combinations and its formula is: nCr = n! / [ r! · (n - r)! ]
Example: how many different groups of 4 persons can you choose from a group of 20 persons?
Since order is not important, use combinations: 20C4 = 20! / [ 4! · (20 - 4)! ] = 20! / [ 4! · 16! ] = 4845.
How many different groups of 4 persons can you choose from a group of 20 persons when order is important -- for instance, you are choosing a president, vice-president, secretary, and treasurer?
Since order is important use permutations: 20P4 = 20! / (20 - 4)! = 20! / 16! = 116280.
(The number of permuations is never smaller than the number of combinations, usually larger, much larger.)
+23246 nPr represents permutations and its formula is: nPr = n! / (n - r)!
Permutations find the number of possibilities when order is important.
When order is not important, use combinations.
nCr represents combinations and its formula is: nCr = n! / [ r! · (n - r)! ]
Example: how many different groups of 4 persons can you choose from a group of 20 persons?
Since order is not important, use combinations: 20C4 = 20! / [ 4! · (20 - 4)! ] = 20! / [ 4! · 16! ] = 4845.
How many different groups of 4 persons can you choose from a group of 20 persons when order is important -- for instance, you are choosing a president, vice-president, secretary, and treasurer?
Since order is important use permutations: 20P4 = 20! / (20 - 4)! = 20! / 16! = 116280.
(The number of permuations is never smaller than the number of combinations, usually larger, much larger.)
