I would greatly appreciate everyone's help with the following (related) probability questions. I believe they involve something called binomial probability but it's been several years since I've taken any math course and don't believe I ever took any math that dealt with these kinds of questions:

On an multiple-choice exam's answer key, what are the chances of a particular answer choice appearing 4 times in a row, assuming there are 5 answer choices (A, B, C, D, & E) and 25 questions on the exam? How many 4-in-a-rows would one expect over the course of 256 25-question exams?

What are the chances of having 2 4-in-a-row occurrences in the same 25-question exam? The letter doesn't have to be the same for each occurrence. How many of these would one expect over the course of 256 25-question exams?

What are the chances of 9 4-in-a-row occurrences over the course of 256 25-question exams? Again, the letter doesn't have to be the same for each occurrences.

What are the chances of a particular 5-answer sequence (such as "ABCDE") occurring 3 times over the course of 256 25-question exams? How many ABCDE sequences would one expect over the course of 256 25-question exams?

By the way, I want to assume that the answer choices are randomly generated (no human bias in avoiding certain sequences).

Thank you very much!