There's no magical number. Any fractions are a consequence of two factors: how many vacancies are available and how many applicants are competing for them. In the past couple of years, I have seen a selection process with six candidates shortlisted for an interview for just one vacancy. I have seen one where there were six candidates for two vacancies. And another one where eight candidates were invited for a sim assessment for six vacancies.
What percentage of the total number of applicants who have submitted a CV are invited for interview is also a highly variable number. It can be close to 100% when the sun is shining and there aren't that many people looking for a new job - or a single digit in a situation like what we're seeing now. It also depends on what resources are involved in said interview. If it's a sim ride, you would only want to invite the most promising candidates for it because sim time is expensive. If it's just a written exam and a chat with one or two people from management, this doesn't require as much resources and can potentially allow for calling in more applicants.