7 different letters are given.Then find the number of ways in which words of 5 letters can be formed such that at least 1 of the letters is repeated.

If all letters are repeated , number of words = 7x7x7x7x7 = 7^5

if none is repated , number of words = 7P5

therefore ,  number of ways when at least one is repated is  7^5 - 7P5