6. 5 letters are to be placed in 5 addressed envelop. Find the probability that

 (i) Each letter is placed correctly

 (ii) More than two letters are placed correctly

 (iii) None of the letters are placed correctly

 

7. 6 balls are to be randomly placed in six cells. Find the probability that

 (i) Only one cell is occupied.

 (ii) Each cell is occupied.

 

8. 4-letters word are formed from the English alphabet. If the repetition of the letters is not allowed, what is the probability that a randomly selected word starts with the letter ‘A'?