How many words with or without meaning can be formed using all the letters of the word ‘EQUATION’ using each letter exactly once?
Additional part: How many of these words begin with E and end with N?
The word is 'EQUATION'
Number of letters = 8 (all distinct)
Number of letters to be used = 8
Number of permutations = 
= 8! = 8 x 7 x 6 x 5 x 4 x 3 x 2 x 1 = 40320
Additional part:
Fix E in box 1 and N in box 8
Number of permutations for box 1 = 
...(i)
Number of permutations for box 8 = 
...(ii)
Number of letters left = 6 
n = 6
Number of boxes left = 6 
r = 6
∴ Number of permutations = 
...(iii)
From (i), (ii) and (iii), by fundamental principle of counting, the toal number of words formed
= 1 x 1 x 720 = 720.
