The number of four-letter words that can be formed with letters a ,   b ,   c such that all three letters occur is

Step-by-step solution

Out of given three letters a ,   b ,   c , we will repeat exactly one of the letter and we can do this in C 1 3 ways. Now, we have four letters and out of these four letters two are identical, so number of ways to arrange these four letters is 4 ! 2 ! . So, the number of four letter words that can be formed with letters a ,   b ,   c such that all three letters occur is C 1 3 × 4 ! 2 ! = 36