For each exam, Ariadne studies with probability 1/2 and does not study with probability 1/2, independently of any other exams. On any exam for which she has not studied, she still has a 0.20 probability of passing, independently of whatever happens on other exams. What is the expected number of total exams taken until she has had 3 exams for which she did not study but which she still passed?

Answer 1

any answer?

Answer 2

30