haksaengdeuri siheomi kkeutnaseo gippeohaeyo.

Because the sentence contains two clauses, and each clause can have its own subject.

• 학생들이 = the subject of 기뻐해요
  → The students are glad
• 시험이 = the subject of 끝나서
  → The exam ended / is over

So the structure is roughly:

• 학생들이
  • [시험이 끝나서]
    • 기뻐해요
• The students
  • because [the exam ended]
    • are glad

This is very normal in Korean. English learners often expect only one subject per sentence, but Korean often has one subject in a main clause and another in a subordinate clause.

-들 is a plural marker. It shows that there is more than one student.

• 학생 = student / students
• 학생들 = students

In Korean, plural is often left unmarked if the meaning is already clear from context. So 학생들이 explicitly says the students, but in some situations Korean might omit -들 and just use 학생이 if the context already makes plurality obvious.

So:

• 학생들이 = clearly plural
• 학생이 = one student, or sometimes a general/student reference depending on context

Here, -들 helps match the English idea of students clearly.

Both are possible, but they have different nuance.

• 학생들이 uses the subject marker -이/가

  • more neutral
  • focuses on who is glad
  • sounds like a straightforward observation

• 학생들은 uses the topic marker -은/는

  • gives a topic or contrast feeling
  • can sound like as for the students...
  • may suggest comparison with someone else

So:

• 학생들이 시험이 끝나서 기뻐해요.
  = a neutral statement: The students are glad because the exam is over.

• 학생들은 시험이 끝나서 기뻐해요.
  = As for the students, they’re glad because the exam is over.
  This could imply that maybe other people are not.

For a basic neutral sentence, 학생들이 is very natural.

끝나서 comes from:

• 끝나다 = to end, to be over
• -아서/어서 = a connector meaning because, so, or sometimes and then

So:

• 끝나다 → stem 끝나-
• 끝나- + -아서 → 끝나서

In this sentence, 끝나서 means because it ended / because it is over.

So 시험이 끝나서 means:

• because the exam ended
• because the exam is over

The exact English wording depends on the translation style, but the Korean form itself is very natural.

Because 끝나다 is an intransitive verb.

That means it describes something ending by itself:

• 시험이 끝나다 = the exam ends / is over

So the exam takes the subject marker -이/가, not the object marker -을/를.

If you want to say that someone finishes something, you usually use the transitive verb 끝내다:

• 학생들이 시험을 끝냈어요 = The students finished the exam

So compare:

• 시험이 끝났어요 = The exam ended / is over
• 학생들이 시험을 끝냈어요 = The students finished the exam

Both can be similar in real-life meaning, but grammatically they are different.

This is a very common learner question.

기뻐하다 is often used for someone else’s observable emotion. Since the students are third person, Korean often prefers 기뻐해요.

• 기쁘다 / 기뻐요 = to be glad, to feel glad
• 기뻐하다 / 기뻐해요 = to show gladness, to be glad

In many textbook-style explanations:

• first person: 저는 기뻐요 = I’m glad
• third person: 학생들이 기뻐해요 = The students are glad

That said, in real conversation, native speakers may sometimes use 기뻐요 for third person too, especially if the emotion is obvious or already known. But 기뻐해요 is a very standard and safe choice here.

The dictionary form is 기뻐하다.

It conjugates like this:

• 기뻐하다 = dictionary form
• stem: 기뻐하-
• 기뻐하 + 아요 → 기뻐해요

This is because 하다 verbs commonly contract like this:

• 공부하다 → 공부해요
• 좋아하다 → 좋아해요
• 기뻐하다 → 기뻐해요

So 기뻐해요 is just the polite present form of 기뻐하다.

In this sentence, it most naturally means because.

• 시험이 끝나서 기뻐해요
  = They are glad because the exam is over

The connector -아서/어서 can sometimes express simple sequence:

• 집에 가서 쉬어요 = I go home and rest

But with an emotion word like 기뻐해요, the causal meaning is the natural one:

• exam ended → students are glad

So here it is best understood as because / since.

Korean normally puts connecting clauses before the final verb of the sentence.

So this pattern is very common:

• reason/event + -아서/어서 + main verb

Here:

• 시험이 끝나서 = because the exam ended
• 기뻐해요 = are glad

The subject 학생들이 can appear before that reason clause, which is what happens here:

• 학생들이 시험이 끝나서 기뻐해요

You could also say:

• 시험이 끝나서 학생들이 기뻐해요

That is also grammatical. It puts more focus on the reason first: Because the exam is over, the students are glad.

So the order is somewhat flexible, but the connected clause still comes before the final main verb.

Because Korean subordinate clauses often do not need a full sentence-final tense ending.

In English, you may think:

• because the exam ended

So you expect a clearly past form. But in Korean, 끝나서 already works naturally in this kind of connected structure.

Also, 끝나다 often has a resultative feel:

• 시험이 끝나서 can mean because the exam ended
• and also naturally imply because the exam is now over

Korean does not always mark tense in exactly the same way English does, especially inside connected clauses.

You may also hear forms like:

• 시험이 끝났으니까 기뻐해요

That sounds more explicitly like since the exam ended / is over.

But 시험이 끝나서 기뻐해요 is completely natural and standard.

A natural pronunciation is approximately:

• 학생들이 → 학쌩드리
• 시험이 → 시허미
• 끝나서 → 끈나서
• 기뻐해요 → 기뻐해요

So the whole sentence sounds roughly like:

• 학쌩드리 시허미 끈나서 기뻐해요

A few sound changes happening here:

• 학생 is pronounced more like 학쌩
• 시험이 often sounds like 시허미
• 끝나서 sounds like 끈나서

These are normal pronunciation changes in spoken Korean.