Ten letters of an alphabet are given. Words with five letters are formed by these given letters. Then the number of words which have at least one letter repeated is

Number of five letter words that can be formed from 10 letters=10×10×10×10×10=105Number of five letter words that have none of their letter repeated=10P5=10×9×8×7×6=30240∴ Number of words which have at least one letter repeated=105−30240=69760