La revista vendió cuatrocientos ejemplares en una semana.

Because vendió is the preterite, which is used for a completed action in the past.

• La revista vendió cuatrocientos ejemplares... = the magazine sold 400 copies, seen as a finished result.
• Vendía would be the imperfect, which usually describes something ongoing, habitual, or backgrounded in the past.

So:

• vendió = sold
• vendía = was selling / used to sell

In this sentence, the focus is on the completed total: 400 copies in one week.

No. Vendió comes from vender and is a regular -er verb in the preterite.

Preterite of vender:

• yo vendí
• tú vendiste
• él/ella/usted vendió
• nosotros vendimos
• vosotros vendisteis
• ellos/ellas/ustedes vendieron

So vendió means he/she/it sold. Here, the subject is la revista, so it means the magazine sold.

The accent in vendió helps mark both stress and the correct verb ending.

Compare:

• vendio = not correct spelling
• vendió = correct, stressed on the last syllable: ven-di-Ó

This is the standard third-person singular preterite ending for many -er and -ir verbs:

• comió
• vivió
• vendió

Yes, revista is a feminine noun, so it takes la in the singular:

• la revista
• las revistas

A native English speaker may want to remember that grammatical gender in Spanish is part of the noun, so the article has to match it.

Here, ejemplares means copies of a publication.

So:

• un ejemplar = one copy
• cuatrocientos ejemplares = 400 copies

This word is especially common for things like:

• books
• magazines
• newspapers

It is a bit more specific than a general word like copias. For a magazine, ejemplares sounds very natural.

Because the sentence is talking about copies of the magazine, not different magazines.

Compare:

• La revista vendió cuatrocientos ejemplares = The magazine sold 400 copies.
• Vendió cuatrocientas revistas could sound like it sold 400 physical magazines, which is understandable, but ejemplares is the more standard publishing term.

So ejemplares is the more natural choice in this context.

Because cuatrocientos agrees with ejemplares, which is a masculine plural noun.

• ejemplar is masculine
• plural: ejemplares
• therefore: cuatrocientos ejemplares

Compare:

• cuatrocientos ejemplares
• cuatrocientas revistas

Hundreds in Spanish must agree in gender with the noun they modify.

Yes. In Spanish, the hundreds are written as single words:

• doscientos
• trescientos
• cuatrocientos
• quinientos, etc.

So cuatrocientos ejemplares is correct.

Because in Spanish, numbers normally go directly before the noun:

• cuatrocientos ejemplares
• tres libros
• veinte personas

You do not say cuatrocientos de ejemplares in a normal sentence like this.

De only appears in other structures, for example after words like millones:

• millones de personas

But with cuatrocientos, no de is used.

Here, en una semana means in one week or within the space of one week.

It gives the time frame in which the result happened: the magazine sold 400 copies over the course of a week.

In many contexts, English might also translate this idea as:

• in a week
• within a week
• over one week

Yes, but the nuance is slightly different.

• en una semana focuses on the result achieved within that period.
• durante una semana emphasizes the duration itself: for a week.

So:

• La revista vendió cuatrocientos ejemplares en una semana = it reached that total within a week.
• La revista vendió cuatrocientos ejemplares durante una semana = also possible, but it sounds more focused on the activity over that week.

In this sentence, en una semana is very natural because the speaker is highlighting the completed sales total.

Yes, it could be changed, but this is the most neutral and standard order:

• Subject + verb + object + time expression

So:

• La revista = subject
• vendió = verb
• cuatrocientos ejemplares = direct object
• en una semana = time phrase

You could also say:

• En una semana, la revista vendió cuatrocientos ejemplares.

That version puts more emphasis on the time frame.

Because the personal a is mainly used with specific human direct objects.

Here, cuatrocientos ejemplares refers to things, not people, so no a is needed.

Compare:

• Vendió cuatrocientos ejemplares.
• Vio a su hermano.

So the absence of a here is completely normal.

Yes. That is another very common way to express the same idea.

• La revista vendió cuatrocientos ejemplares en una semana = The magazine sold 400 copies.
• Se vendieron cuatrocientos ejemplares en una semana = 400 copies were sold in a week.

The second version is more impersonal and shifts focus away from la revista as the subject. Spanish often uses this se construction where English might use a passive.

A simple pronunciation guide for Spain Spanish would be:

la re-BEES-ta ben-DYÓ kwa-tro-SYEN-tos e-hem-PLA-res en OO-na se-MA-na

A few helpful points:

• revista: the v sounds close to b
• vendió: stress the last syllable: -dió
• cuatrocientos: stress on -cien-
• ejemplares: in much of Spain, j sounds like a strong English h
• c before i in Spain is often pronounced like th in think, so cientos sounds roughly like thientos

Yes. Spanish, like English, often uses the publication or company as the subject in this kind of sentence.

So la revista vendió... is understood as:

• the magazine sold that many copies
• the magazine’s publication/distribution achieved that number

It is a normal kind of shorthand, just like English says:

• The magazine sold 400 copies
• The book sold well

Even though the object itself is not acting like a person, the sentence is perfectly natural.