Permutation and CombinationHard
Question
10 different letters of an alphabet are given. Words with 5 letters are formed from these given letters, then the number of words which have atleast one letter repeated is:
Options
A.69760
B.30240
C.99748
D.none
Solution
Number of words which have at least one letter repeated = total words - number of words
which have no letter repeated = 105 - 10 × 9 × 8 × 7 × 6 = 69760
which have no letter repeated = 105 - 10 × 9 × 8 × 7 × 6 = 69760
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