What's a common misuse of the comma?

There are lots of ways to misuse the comma, but probably the most common is using a comma between two items joined by and when they aren't full sentences:

Our new computers will be fast, and will arrive in less than a week.

To correct the problem, you can take out the comma:

Our new computers will be fast and will arrive in less than a week.

Or you can make the second part a full sentence:

Our new computers will be fast, and they will arrive in less than a week.

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