Ok does anyone know how to go about this problem?
I believe all you have to do for this problem is take the total number of ways to permute the 26 letters of the alphabet , which is 26!, and subtract all of the strings which contain the words 'fish', 'cat', and 'bird'. Namely if A='fish', B='cat', and C='bird' - |A or B or C| = |A| + |B| + |C| - |A and B| - |A and C| - |B and C| + |A and B and C|.
