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# Permutation

Can any one please tell me with example the permutation ? Thanks

P(n,r) = n!/(n-r)!
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mustish1
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3 Solutions

Commented:
P (10,2)  = 10! / (10-2)!  = 10! / 8! = (10*9*8*7*6*5*4*3*2*1)/(8*7*6*5*4*3*2*1) = 10*9 = 90
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Commented:
Example - if you have to select 2 numbers out of 10 -

P (10,2)  = 10! / (10-2)!  = 10! / 8! = (10*9*8*7*6*5*4*3*2*1)/(8*7*6*5*4*3*2*1) = 10*9 = 90
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Author Commented:
Where we use permutation
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Commented:
as an example,    10  letters (abcdefghij), taken 2 at a time

1      ab
2      ba
3      ac
4      ca
6      da
7      ae
8      ea
9      af
10      fa
11      ag
12      ga
13      ah
14      ha
15      ai
16      ia
17      aj
18      ja
19      bc
20      cb
21      bd
22      db
23      be
24      eb
25      bf
26      fb
27      bg
28      gb
29      bh
30      hb
31      bi
32      ib
33      bj
34      jb
35      cd
36      dc
37      ce
38      ec
39      cf
40      fc
41      cg
42      gc
43      ch
44      hc
45      ci
46      ic
47      cj
48      jc
49      de
50      ed
51      df
52      fd
53      dg
54      gd
55      dh
56      hd
57      di
58      id
59      dj
60      jd
61      ef
62      fe
63      eg
64      ge
65      eh
66      he
67      ei
68      ie
69      ej
70      je
71      fg
72      gf
73      fh
74      hf
75      fi
76      if
77      fj
78      jf
79      gh
80      hg
81      gi
82      ig
83      gj
84      jg
85      hi
86      ih
87      hj
88      jh
89      ij
90      ji
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Commented:
When you need to calculate the number of possibilities is where you need permutation.
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Commented:

permutations observe order

"ab"  and "ba" are distinct results

combinations ignore order

"ab" and "ba"  are the same result
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Author Commented:
looks like something probability
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Commented:
yes,  what are the odds of drawing an "a" and a "b" out of 10 letters?

90 possible permutations,  "ab" and "ba" are the successes   so    2/90
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Commented:
the act of changing the order of elements arranged in a particular order, as abc into acb, bac, etc., or of arranging a number of elements in groups made up of equal numbers of the elements in different orders, as a and b in ab and ba; a one-to-one transformation of a set with a finite number of elements.

Example: The permutations of the letters in the set {a, b, c} are:
P (3,3)  = 3! / (3-2)!=3x2x1/2x1=6

abc        acb
bac        bca
cab        cba
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Commented:
the act of changing the order of elements arranged in a particular order, as abc into acb, bac, etc., or of arranging a number of elements in groups made up of equal numbers of the elements in different orders, as a and b in ab and ba; a one-to-one transformation of a set with a finite number of elements.

Example: The permutations of the letters in the set {a, b, c} are:
P (3,3)  = 3! / (3-3)!=3x2x1/1=6

abc        acb
bac        bca
cab        cba

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