Learn Hardcore Chinese: tā hé shìyǒu zài túshūguǎn fùxí le sān gè xiǎoshí le, hái bù xiǎng huí jiā. - She and her roommate have been reviewing in the library for three hours and still don’t want to go home.

The first 了 (after 复习) is the perfective 了. It marks that the action “review” has actually happened: 复习了 = “reviewed / have reviewed”.
The second 了 at the end of the clause (三个小时了) is the sentence-final 了, which often carries the meaning “already / up to now / a change of situation”.

Together, 复习了三个小时了 suggests:
“They have already spent three hours reviewing (up to now).”

So the pattern is: Verb + 了 + Duration + 了 → “have been doing X for [duration] (already / up to now).”

Can I remove one of the 了’s? How does the meaning change?

Keep both (original):
- 复习了三个小时了
  Emphasizes both completion of that three‑hour period and the idea of “already / up to now”.
  → “(They) have already been reviewing for three hours.”
Remove the first 了: 复习三个小时了
- Much less common and can sound a bit off or at least less natural.
- Native speakers normally keep the first 了 in this pattern.
Remove the last 了: 复习了三个小时
- Just states the duration of a completed action: “reviewed for three hours.”
- It doesn’t clearly carry the “up to now / already” nuance, and it doesn’t so strongly imply the situation is still ongoing.
Remove both: 复习三个小时
- Not really natural as a complete sentence describing a past event; it sounds more like a plan (“review for three hours”).

For “have been doing X for three hours (already)”, the standard, very natural pattern is: V 了 + Duration + 了.

Does 复习了三个小时了 mean they are still reviewing now, or that they finished?

In this sentence it mostly implies they are still at the library and the situation continues:

复习了三个小时了 by itself usually means “have been reviewing for three hours (up to now)”, often with the action still in progress.
The next part 还不想回家 (“still don’t want to go home”) reinforces the idea that they are still there, not finished and gone.

So the default reading here is: They have already been reviewing for three hours and are still there; they still don’t want to go home.

In other contexts, the same structure can sometimes be interpreted as “had done X for three hours (by that time)”, but with 了…了 + 还… it’s usually “up to now and still relevant/ongoing.”

What exactly does 还 mean in 还不想回家?

Here 还 (hái) means “still / even now”.

不想回家 = “don’t want to go home.”
还不想回家 = “still don’t want to go home / don’t want to go home yet.”

So the sentence is:
“They have already been reviewing for three hours, and (even after that) they still don’t want to go home.”

Note: 还 can also mean “also” or “in addition” in other contexts, but with a negative like 还不… it usually has the “still not / not yet” feeling.

What’s the difference between 还不想回家 and 还没回家?

还不想回家
- Focus: their desire / intention.
- Meaning: “They still don’t want to go home (yet).” Maybe they enjoy studying, or feel they should study more.
还没回家
- Focus: the fact that they have not gone home.
- Meaning: “They still haven’t gone home yet.” It says nothing about whether they want to or not.

So:

还不想回家 → “still don’t feel like going home.”
还没回家 → “still haven’t gone home (fact).”

You can combine them too:
复习了三个小时了，她还没回家。
“She has been reviewing for three hours, and she still hasn’t gone home.”

Why do we use 不想回家 and not 不要回家 or 不回家?

These express slightly different ideas:

不想回家
- 想 = “want / feel like.”
- 不想回家 = “doesn’t want to go home.”
- Talks about inner desire / intention.
不回家
- Literally “(she) is not going home / does not go home.”
- States a decision or fact, not explicitly about “want”.
不要回家
- This often sounds like a command: “Don’t go home.”
- Or in reported speech: “(She says) she doesn’t want to go home” (less common; 不想 is clearer for “don’t want to”).

In this sentence we’re describing how she feels after three hours of review, so 不想回家 (“still doesn’t want to go home”) is the most appropriate.

Why do we say 三个小时 with 个? Is 个 really needed?

Yes, 小时 (hour) normally takes the measure word 个:

一个小时 – one hour
两个小时 – two hours
三个小时 – three hours

So 个 is the standard measure word used with 小时 in everyday speech.

You can sometimes hear 三小时, especially in formal or written language, but 三个小时 is more natural and common in spoken Mandarin. For a learner, it’s safer to always say X个小时.

Why is the word order 在图书馆复习了三个小时了 and not something like 复习了三个小时在图书馆?

Chinese word order usually follows this pattern:

[Time] + [Place] + [Manner] + Verb + Object

Here:

在图书馆 = place phrase (“at the library”)
复习 = verb (“review”)
三个小时 = duration

So we put it as:

在图书馆复习了三个小时了
“(She) at-the-library reviewed for three hours (already).”

Putting 在图书馆 after the verb + duration (like 复习了三个小时在图书馆) is ungrammatical or at least very unnatural in standard Mandarin.

So: place phrase (在图书馆) normally comes before the verb, not at the end.

Why do we use 在 before 图书馆, but not before 家 in 回家?

在图书馆 is a location phrase: “at the library.”
Here 在 is used like a preposition: “at / in”.
回家 is a verb–object compound meaning “go home / return home.”
- 回 = return
- 家 = home
  Together they form a set phrase; you don’t usually say 回在家.

So:

To say where an action happens (study, eat, work): use 在 + place.
- 在图书馆复习 – review at the library
- 在家学习 – study at home
To say return home, you just say 回家, no 在 needed.

What is the function of 和 in 她和室友? Could I say 跟室友 or 和她的室友?

和 (hé) here means “and / with”.
她和室友 literally = “she and (her) roommate” → “she and her roommate”.

You can also say:

她跟室友在图书馆复习… – 跟 (gēn) is another very common “with / and” word in speech.
她和她的室友在图书馆复习… – explicitly “she and her roommate”.
Usually the second 她的 is omitted when the context is clear.

All of these are grammatical. The original 她和室友… is concise and perfectly natural: the roommate is assumed to be her roommate from context.

Where could I put 已经 in this sentence, and how would that change the tone?

Most natural positions:

她和室友已经在图书馆复习了三个小时了，还不想回家。
她和室友在图书馆已经复习了三个小时了，还不想回家。

Both mean roughly:
“She and her roommate have already been reviewing at the library for three hours and still don’t want to go home.”

已经 (yǐjīng) explicitly adds the sense of “already,” emphasizing that the amount of time is substantial or surprising.
The sentence-final 了 already has an “up to now / already” feeling, so adding 已经 makes that emphasis even stronger, a bit like stressing in English:
“They’ve already been studying for three hours and still don’t want to go home!”