-- The first letter can be either one of 2 letters ('i' or 'o'). For each of those ...
-- The second letter can be any one of the remaining 4 . For each of those ...
-- The third letter can be any one of the remaining 3 . For each of those ...
-- The fourth letter can be any one of the remaining 2 . For each of those ...
-- There's only 1 letter left to go into the fifth place.
Total possible arrangements = (2 x 4 x 3 x 2 x 1) = 48 possibilities.
