El trabajador

That's right Meghan, nouns that en in -or are generally masculine, but if they can also refer to a woman, like trabajador or inversor, then they take the -a (la trabajadora, la inversora) and the -as for their plural (unas trabajadoras, unas inversoras).

Un saludo

Inma

Hi again Meghan,

Here is a lesson connected to your query about "trabajador". It is about adjectives, but it will clarify it a bit more. 

Forming the singular and plural of adjectives ending in -án, ón, -or

Inma