Is this a geometric distribution problem? Suppose a student starts with test A, and will proceed to test B, then test C if he passes.
The probability for the student to pass test A is 30%.
The probability for the student to pass test B is 20%.
The probability for the student to pass test C is 10%.
The student has maximum 20 tries to attempt for the tests in TOTAL.
How do I calculate the probability of the student to pass test C, starting from test A, within 20 tries? My hunch is using geometric distribution but I am rather unsure since this problem involves multiple different "stages" with each stage having different probabilities.
Clarification: If the student passes test A, he does not have to take A again, and can use the remaining attempts (20 minus attempts used to pass A) for B and C. Same goes for B.

No.
Since the probabilities are different at each time point, this data will not follow a geometric distribution.
I also don't quite understand when you say "The student has maximum 20 tries to attempt for the tests in TOTAL." bit, but that's not necessary to answer your question.
