Need help designing ER Diagram

I am not a database engineer, I am just getting started with designing data models.

A User registers to my application. My application has Funds that are predefined with an InvestmentStrategy. A user deposits cash into their account Bankroll. A user invests from their Bankroll into a Fund or multiple. A fund buys into Investments. A User selects Picks to guide the InvestmentStrategy. The InvestmentStrategy uses historical Pick evidence by User to determine which Investments to make. Investments have Results, which pay Users based on performance. A User can leave a Fund. A User can withdraw from their Bankroll. A InvestmentStrategy can also pay percentage of profit to User.

This leads to a wide array of circular relationships. I am having a hard time drawing an ER diagram describing the entities and relationships above. Does anyone have examples or suggestions for how to create their model? Thanks!

Why does this finite state machine state transition diagram solution has more states than my solution?

I can’t figure out what is wrong with my solution and why does it differ from book’s solution. I think the only thing that matters is the previous state of A so that there should be two states, one for previous A=0 and one for previous A=1. Where am I mistaken? I would really appreciate any explanation.

this is the question

this is book's solution here

this is my solution

Is my use case UML diagram too complicated?

The user of my app has access to two tools within my app. Each tool is comprised of multiple tables that the user has to fill with information.
The app is more complex but that’s roughly what’s it’s about.
This is the UML Diagram that I have designed based on the app:
enter image description here I am wondering whether the use case diagram should be designed otherwise. Maybe, I should design the use case diagram for each tool independently. That way, it will be less cumbersome.
But, this will mean that each tool represents its own system. And I don’t know if from a UML viewpoint, that is the right thing to do.

Sequence diagram, main scenario of use case “Register Company”

enter image description here

About the Sequence Diagram above, judge the following items:

I.The internal actor is the “Company”, which is responsible for informing the data to perform the business registration.

II.As initial interface, the class “Register Company” is used. To register the companies, it is understood that the objects “Branch of Activity” and “Zip Code” are already registered.

For each object represented, it can be seen that a “lifeline” has begun, and when the object begins to interact, the focus of control is used, which has its messages in a numbered and orderly manner.

IV.After the execution of the operations, the receiving object “Company” sends a return message to the sender interface “Form_Cadastrar Empresa”, represented in the dashed line.

The correct items are:

Sequence Diagram Assistance with external database

I have 5 Java/android classes which are in sequential order. The user inputs data into the text box and clicks next. Two things happen, 1 the data the user inputs is passed to the next activity and it is also inserted into an external database.

The same things happens on each of the 5 activities. I’m struggling to represent this in a sequence diagram form. All the sequence diagram examples I see dont have an external database involved in every class/activity and my diagram only moves forward, most diagrams have methods moving back and forth.