{"id":4049,"date":"2021-08-15T12:49:52","date_gmt":"2021-08-15T12:49:52","guid":{"rendered":"https:\/\/mathemerize.com\/?p=4049"},"modified":"2021-11-27T21:59:29","modified_gmt":"2021-11-27T16:29:29","slug":"permutation-combination-formula","status":"publish","type":"post","link":"https:\/\/mathemerize.com\/permutation-combination-formula\/","title":{"rendered":"Permutation and Combination Formula – Properties"},"content":{"rendered":"
Here you will learn formula permutation and combination and properties of permutation and combination with examples.<\/p>\n
Let’s begin –<\/p>\n
Each of the arrangements in a definite order which can be made by taking some or all of the things at a time is called a PERMUTATION. In permutation, order of appearance of things is taken into account; when the order is changed, a different permutation is obtained.<\/p>\n
Generally, it involves the problems of arrangements (standing in a line, seated in a row), problems on digit, problems on letters from a word etc.<\/p>\n
\n\\(^{n}P_r\\) denotes, the number of permutations of n different things, taken r at a time (n \\(\\in\\) N, r \\(\\in\\) W, r \\(\\le\\) n)<\/p>\n
\\(^{n}P_r\\) = n(n – 1)(n – 2)……..(n – r + 1) = \\(n!\\over (n-r)!\\)<\/p>\n<\/blockquote>\n
Note :<\/strong><\/p>\n
(i) \\(^{n}P_n\\) = n!, \\(^{n}P_0\\) = 1, \\(^{n}P_1\\) = n<\/p>\n
(ii) Number of arrangements of n distinct things taken all at a time = n!.<\/p>\n
(iii) \\(^{n}P_r\\) is also denoted by P(n,r).<\/p>\n
Combination<\/h2>\n
Each of the groups or selections which can be made by taking some or all of the things without considering the order of the things in each groups is called a COMBINATION.<\/p>\n
Generally, involves the problem of selections, choosing, distributed groups formation, committee formation, geometrical problems etc.<\/p>\n
\n\\(^{n}C_r\\) denotes the number of combinations of n different things taken r at a time (n \\(\\in\\) N, r \\(\\in\\) W, r \\(\\le\\) n)<\/p>\n
\\(^{n}C_r\\) = \\(n!\\over r!(n-r)!\\)<\/p>\n<\/blockquote>\n
Note :<\/strong><\/p>\n
(i) \\(^{n}C_r\\) is also denoted by \\(\\binom{n}{r}\\) or C(n,r).<\/p>\n
(ii) (ii) \\(^{n}P_r\\) = \\(^{n}C_r\\).r!<\/p>\n\n\n
Example : <\/span> How many four letter words can be formed from the letters of the word ‘ANSWER’ ? How many of these words start with vowel ?<\/p>\n
Solution : <\/span> Number of ways of arranging 4 different letters from 6 different letters are
\n\t\t \\(^{6}C_4\\).4! = 360
\n\t\t There are two vowels (A & E) in the word ‘ANSWER’
\n\t\t Total number of 4 letter words starting with A : A _ _ _ = \\(^{5}C_3\\).3! = 60
\n\t\t Total number of 4 letter words starting with E : E _ _ _ = \\(^{5}C_3\\).3! = 60
\n\t\t \\(\\therefore\\) Total number of 4 letter words starting with a vowel = 60 + 60 = 120
\n\t\t <\/p>\n\n\nProperties of Permutation and Combination<\/h2>\n
(a) The number of permutation of n different objects taken r at a time, when p particular objects are always to be included is r!.\\(^{n-p}C_{r-p}\\) (\\(p\\le r\\le n\\)).<\/p>\n
(b) The number of permutation of n differnt objects taken r at a time, when repetition is allowed any number of times is \\(n^r\\).<\/p>\n
(c) Following properties of \\(^{n}C_r\\) should be remembered:<\/p>\n
(i) \\(^{n}C_r\\) = \\(^{n}C_{n-r}\\); \\(^{n}C_0\\) = \\(^{n}C_n\\) = 1<\/p>\n
(ii) \\(^{n}C_x\\) = \\(^{n}C_y\\) \\(\\implies \\) x = y or x + y = n<\/p>\n
(iii) \\(^{n}C_r\\) + \\(^{n}C_{r-1}\\) = \\(^{n+1}C_r\\) <\/p>\n
(iv) \\(^{n}C_0\\) + \\(^{n}C_1\\) + \\(^{n}C_2\\) + ………. + \\(^{n}C_n\\) = \\(2^n\\)<\/p>\n
(v) \\(^{n}C_r\\) = \\(n\\over r\\)\\(^{n-1}C_{r-1}\\)<\/p>\n
(vi) \\(^{n}C_r\\) is maximum when r = \\(n\\over 2\\) if n is even & r = \\(n-1\\over 2\\) or r = \\(n+1\\over 2\\), if n is odd.<\/p>\n
(d) The numbers of combinations of n different things taken r at a time,<\/p>\n
(i) when p particular things are always to be included = \\(^{n-p}C_{r-p}\\)<\/p>\n
(ii) when p particular things are always to be excluded = \\(^{n-p}C_r\\)<\/p>\n
(iii) when p particular thing are always to be included and q particular things are to be excluded = \\(^{n-p-q}C_{r-p}\\)<\/p>\n\n\n
Example : <\/span>There are 6 pockets in the coat of a person. In how many ways can he put 4 pens in these pockets?<\/p>\n
Solution : <\/span>First pen can be put in 6 ways.
\n Similarly each of second, third and fourth pen can be put in 6 ways
\n Hence total number of ways = \\(6\\times 6\\times 6\\times 6\\) = 1296.
\n\t\t <\/p>\n\n\n\n