SCRUM GUIDE 2020: Number of Scrum Masters for one product

Don't see any edit button here. There is a small correction

Developers Group 1 (1 >= and <= 10)

For any given Product, there should be exactly one Product Owner and exactly one Product Backlog. If multiple teams are working on the same Product then these will be shared.

At any given time, it should be transparent to all team members who their Product Owner is, and who their Scrum Master is, so the accountabilities are clear.

I would agree with your assessment that there should be one Product Backlog, Product Goal, and Product Owner for multiple Scrum Teams working on a single product. However, I wouldn't necessarily say that you would only have multiple Scrum Masters if the Scrum Master is also serving the team in a different capacity. There are a lot of factors that go into how many teams a Scrum Master can work with, including the experience and maturity of the Scrum Master and the maturity of the teams.

In my experience, a skilled, experienced Scrum Master can effectively work with up to 3 or 4 teams if those teams are very mature and can generally function with mostly hands-off coaching and those teams are working on a single product. As soon as you have multiple products, teams that need more intensive or hands-on coaching, or an inexperienced Scrum Master, the number of teams that can be supported by a Scrum Master goes down. Someone performing a dual role (such as a Scrum Master who is also a Developer) will also limit the number of teams, probably down to 1.

Thanks for the explanation Ian and Thomas.

So what I understand is there may be multiple Scrum masters working on the same product and that does not violate the Scrum....

Product

    Product Owner

    Team 1 > Developers

    Team 2 > Developers

    Team 3 > Developers

    (...)

    Team N > Developers

You must have as much scrum masters as necessary to serve all teams as a servant-leader. If you have, for example, 10 teams, only one scrum master will not be able to observe all teams, attend to all retrospectives, reviews, talk and listen to people, remove impediments, etc. 

For PSM-1 is important to know what @Ian said on his comment.

It is important to be clear to you that more teams, more dependencies and scale issues.

Take a look at the PSM-1 topics, i don't think that multiple teams should be a topic to your PSM-1. 

The important point is:

One Product > One Product Owner > One Product Backlog. 

So what I understand is there may be multiple Scrum masters working on the same product and that does not violate the Scrum....

You are right. Multiple teams will require multiple Scrum Masters. It is ok to scrum guide, but not that simple in a real world. Take a look at Nexus framework (SPS). 

Thank you Tiago for the explanation.

I understand the complexity part and hence wanted to clarify from the exam point of view. Do you recommend reading Nexus guide for PSM-1?