It depends on all sorts of factors.

With debut fiction, the agents I've asked have mostly said that they sell about half of the new authors they take on. However, this doesn't mean that if you're taken on by an agent you have a 50% chance of being published, because so much depends on the book and how it's submitted. Every book is different. Some are so good that they get multiple offers of representation, and multiple offers of publication; others barely scrape their way onto an agent's lists, and might well struggle to go further.

Established authors who have a track record with their agent, and who are represented by a good agent, are more likely to get most of their books published--perhaps all, if their agent is proactive, discusses with them how best to proceed and what books are going to sell well, and so on.

Authors with one or two books published, and lacklustre sales, might find themselves unable to find a deal.