Spanish language Q&A Forum

I have gotten confused by a specific use of the personal a.  As I understand it, if you are mentioning a person or group of people, you need a personal a infront of the person.  For example if I am talking about a reporter mentioning Juan, I might say El reportero mencionó a Juan.  It also looks like if I want to say that the reporter mentioned Juan to Ana, I should say  El reportero mencionó Juan a Ana.  

Is this correct?  Is this also a general pattern - i.e. when I would normally use a personal a, but there is an indirect object (Ana), should I always drop the personal a and use the a for the indirect object?

Thanks

Is there a difference between the above options?  It looks like they can be used interchangeably, but I'm not sure.  Here are the examples:

Van a construir un hotel cien por cien ecológico.

Estoy seguro al ciento por ciento.

Thanks!

Why "cada uno de april" versus "cada primero de abril"? How common is either form?

What is the difference between these 2? Both are expressing action in progress but I'd like to be more clear about when we would use each.

What about the (even in English) problematic decade of 2000-2009? 

or 2010-2019 ?