Quantitative Aptitude Practice Test: Permutations and Combinations — Flashcards

Here are some formulas for permutations and combinations: 

Permutations: The formula for permutations is nPr = n!/(n-r)! . 
Permutations are used for lists of data where the order of the data matters. 

Combinations: The formula for combinations is nCr = n!/[r! (n-r)!]. 
Combinations are used for groups of data where the order of the data doesn't matter. 

Number of ways to arrange \(r\) things out of \(n\) different things: The formula is nPr = n! (n−r)! . 
Number of ways to select \(r\) things out of \(n\) given things wherein \(r\le n\): The formula is nPr = r!×nCr. 
nCn = 1 and nC0 = 1 
nCr = nC. (n - r):  
(n-1)! ways: If 'n' objects are arranged in a circular way and if the clockwise and anti-clockwise arrangement is different. 
C (n+ r -1 ,r) = (n + r -1 )! / r! (n – 1) !: