1. I got a C- on the math test.

Reading: C - : C minus (right?)

2. The math problems are difficult to solve.

3. The math questions are difficult to solve.
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Are both OK?

1. Yes, you're right about the pronunciation.

2 and 3 are both fine, yes.

Yes, both "The math problems are difficult to solve" and "The math questions are difficult to solve" are grammatically correct and have similar meanings. Both sentences convey the idea that the math problems or questions are challenging to solve. The choice between "problems" and "questions" depends on the context and what specifically you are referring to. If you are discussing a specific set of math problems, then "problems" would be more appropriate. If you are talking about a general difficulty with math questions as a whole, then "questions" would be more suitable.