A probability problem, not sure whether this is a combination problem or permutation.
A test consists of 5 questions. A correct answer scores 2 marks and an incorrect one, to penalize guessing, scores -1. Assuming that all the questions are answered, find probability of scoring -2.
I figured that only way to score -2 is 1 correct and 4 incorrect, 2 - 4 = -4. All other combinations are incorrect.
Stuck here, Can you guys give me a hint on how to proceed further? Thanks!