I remember somebody correcting me once when I said, "Two and two makes four", since the conjunction and would imply the use of a plural verb. They would prefer I said:
Two and two make four.
I've been thinking about it and wondering if one or the other is correct, or if both are. It would seem that using the plural verb is grammatical. However, I've heard the singular verb being used more often and feel that it is correct. Is there some exception about using the singular verb in logical statements and mathematical formulae?