Spanish language Q&A Forum

I think the conjugation of servir in this lesson seems to be incorrect, it leaves off the s in all forms, except in the nosotros form i where it leaves off the root ser.  

When do we not use the articles like "en casa" instead of "en la casa"?

“Usted tendría que devolver los

artículos en la caja. (You would have

to return the articles at the till.)

HINT: Conjugate "tener que"' in El

Condicional Simple.

“No entiendo “the till.” In the US would be the cashier, I think. In Latin America, perhaps “el cajero.” “The till” has various contations in the US and some border on the negative. From Miriam-Webster: 

till

 noun (1)

Definition of till (Entry 4 of 5)

I see that “el” and “la” are based off masculine or feminine. How do I know if a general noun (e.g. car) is masculine or feminine tense?

In one question, I was tasked to translate "I want to buy it for him."     I selected " Quiero se lo comprar."   and was marked wrong.   I understand that one could say "Quiero comprárselo." , which was the correct answer.   But I always thought that you could have the pronouns attached to the infinitive or put them in front.   

A little off topic, but consider:

1. donde, adonde/a donde

2. dónde, adónde/a dónde

and for that matter (or maybe especially for the case of), 

3. quizá, quizás 

Within each group the various options can be used interchangeably. But what factors influence the chosen form? For example do some people tend to use the same form all the time? Do people just randomly use all the forms equally? Do some localities tend to use one form more than others? Is there a pronunciation efficiency issue (similar to y and i  or  o and u, but not a hard-and-fast rule)?

I guess my questions especially apply to quizá versus quizás.