I have a question for a challenge that I'm trying to create - having some trouble quantifying the size of the challenge's test bank.
- 20 people are taking a challenge of 9 questions
- the test bank (n) doesn't change. so when a new challenge starts it draws from the same test bank (the questions are not replaced by new ones). within a challenge, however, there are 9 unique questions.
- I need to determine the size of the question bank (n) that yield the acceptable rate of repeats, which is 3 repeats with a probability of 95%.
I previously used combinatorics to solve a problem like this, but I couldn't find out how to correctly integrate the number of people, in this case 20, taking the challenge.