Ten different letters of an alphabet are given. Words with five letters are formed from these given letters. Determine the number4 of words which have at least one letter repeated.

Options

A. `10^(5)`
B. 30240
C. 69760
D. none of these

Explanation

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`.