6 different letters of an alphabet are given. Words with four letters are formed from these given le

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6.Permutation and Combination

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$6$ different letters of an alphabet are given. Words with four letters are formed from these given letters. Then the number of words which have atleast one letter repeated and no two same letters are together, is

A

$390$

B

$360$

C

$240$

D

$150$

Solution

$2$ diff. $2$ same : $^6C_1.^5C_2.2!.^3C_2 = 360$

$2$ same $2$ same : $^6C_2.2 = 30$

Total $390$

Standard 11

Mathematics

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