In the Land of Oz only one or two-letter words are used. The local language has 68 different letters. The parliament decided to forbid the use of the seventh letter. How many words have the people of Oz lost because of the prohibition?	Choose the correct choice from the following answers.
A) 65  B) 66  C) 67  D) 131  E) 136
The answer to the question is indeed E. The problem with above solutions is that they do not consider words like AA, BB, ...   The number of 1 letter words (X) that can be made from 68 letters is 68;   The number of 2 letter words (XX) that can be made from 68 letters is 68*68, since each X can take 68 values.   Total: 68+68*68.   Similarly:   The number of 1 letter words (X) that can be made from 67 letters is 67;   The number of 2 letter words (XX) that can be made from 67 letters is 67*67, since each X can take 67 values.   Total: 67+67*67.   The difference is (68+68*68)-(67+67*67)= 
<gadget id="calculator">(68+68*68)-(67+67*67)</gadget>
<output>136</output>
136.   Answer: 136.
<result>E</result>
In the Land of Oz only one or two-letter words are used. The local language has 68 different letters. The parliament decided to forbid the use of the seventh letter. How many words have the people of Oz lost because of the prohibition?