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Ten different letters of an alphabet are given. Words with five lettersare formed from these given letters. Determine the number4 of words whichhave at least one letter repeated.A. `10^(5)`B. 30240C. 69760D. none of these

Answer» The total number of 5-letter words which can be formed from 10 letters when one or more of its letters is repeated `=10xx10xx10xx10xx10=10^(5)`.
The total number of 5-letter words when none of their letters is repeated `=^(10)C_(5)xx5!""=30240`.
Hence, the number of 5-letter words which have at least one of their letters repeated `=10^(5)-30240=69760`.


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