As a master student, our class is getting assigned homework weekly as part of a statistics related module. These assignments are graded and will contribute to the final mark with a weight of 70%. There are around 10 of these assignments and the average of them is used.
Now, I discovered that a partial solution to one of the assignments is available inside the class material. This is inside a file that is not really accessed by everyone since it is provided by the teacher for the students elaborating theirs answers with a certain software. I strongly believe that these parts were put online by mistake and the teacher or its assistant do not know about this.
Is it ethical to withhold this fact from my classmates and use the additional knowledge in my favour?
Do I have an ethical 'obligation' to report this to the teacher so he knows in advance to adjust the grading accordingly?
Basically, the information is there for everyone to access, still I believe that I should notice the teacher about the mistake so they can inform the class and remedy this in an academically worthy manner.