I am not happy with my new Zippy 700 mountain bike because it has the following problems the back tire does not match the front tire, and the leather seat has a hole in it.

Use a colon after “the following problems” because the words that follow list the problems. The sentence should read: “I am not happy with my new Zippy 700 mountain bike because it has the following problems: the back tire does not match the front tire, and the leather seat has a hole in it.” A semicolon would not be the right mark to introduce this list.

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