題組內容
1. (15%) Suppose that a "word" is any string of seven letters of the alphabet {A, B, C ..., Z}, with repeated letters allowed. Answer the questions.
(b) How many words begin with A or end with B?
1. (15%) Suppose that a "word" is any string of seven letters of the alphabet {A, B, C ..., Z}, with repeated letters allowed. Answer the questions.
(b) How many words begin with A or end with B?