Exam questions have two wonderful property: they have an answer, and the person who wrote it knows that you have the knowledge to find the answer.
The best professors strike and ignore questions that "failed", ie didn't accurately test what they thought they would.
This isn't always true. The person who wrote it only knows what they taught, not what you have learned. The point of the test is to find what you have learned.
This is just a nitpick I think.