Answer:
It depends
Explanation:
It depends on how many problems are in the test. If the test has a standard amount of ten questions, you can only miss one question if you want to get a solid 90%. If the test has twenty questions, you can miss two to get that 90%.
If you're going for an 80% (or B), you can miss two on a ten-question test and four on a twenty-question test.
Again, it all depends on the number of questions and what percentage you want to get on the test.