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rbmix.com |
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Permutations and combinations
n ! is read as n factorial and is defined as
n ! = n ( n-1) ( n-2) ( n-3) . . .3.2.1 , if n is a positive integer
0 ! = 1
n Pr or P(n,r) is the number of ways of arranging n things taken r at a time, where n is greater than or equal to r.
n
Pr =
n C r or C(n,r) is the number of combinations of n things taken r at a time . n C r is the number of ways of selecting r things from n things.)
n
C r =
Note:
n C r = n C(n-r)
nC(r-1) +nCr = (n+1) C r
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