Learn Hardcore Indonesian: Beberapa pelajar SMA datang ke kelas ini; guru menggunakan campuran bahasa Indonesia dan Inggris ketika menjelaskan konsep yang sulit. - Several high-school students come to this class; the teacher uses a mix of Indonesian and English when explaining concepts that are difficult.

It usually suggests more than one, but not many.
In English you might translate it as:
- some high school students
- a few high school students
- several high school students

Context decides which English word sounds most natural, but in Indonesian beberapa itself is neutral among those options.

Is pelajar singular or plural here? Why isn’t there any plural ending like in English?

Indonesian nouns usually do not change form for singular vs plural.

pelajar can mean student or students, depending on context.
In beberapa pelajar SMA, beberapa already shows it’s more than one, so pelajar is understood as students.

If you really want to emphasize plurality, you can say:

para pelajar SMA – a group of students (slightly formal)
pelajar-pelajar SMA – plural by repetition, but often unnecessary and can sound a bit heavy in everyday speech.

What does SMA mean, and is pelajar SMA the same as “high school students”?

SMA stands for Sekolah Menengah Atas, which is roughly equivalent to senior high school.

pelajar SMA = senior high school students / high school students
Common alternatives with slightly different flavor:
- siswa SMA – very common, sounds neutral and natural
- murid SMA – also used, but murid is a bit more basic/“pupil”-like
- anak SMA – literally high school kids, more casual/colloquial

All of these would usually be understood as high school students.

Why is it datang ke kelas ini, not datang di kelas ini?

In Indonesian:

ke = to / toward (movement)
di = in / at / on (location, no movement)

datang (to come) is a movement verb, so it takes ke:

datang ke kelas ini = come to this class (moving toward)
di kelas ini = in this class (already there, describing location)

So:

Beberapa pelajar SMA datang ke kelas ini = Some high school students come to this class.
After they arrive, you could say: Mereka sudah di kelas ini = They are already in this class.

How do we know if guru menggunakan means uses or used? There is no tense marker.

Indonesian verbs generally do not change for tense (past, present, future).

guru menggunakan can mean:

the teacher uses (present / habit)
the teacher is using (present continuous)
the teacher used (past)

The actual time is understood from context or from time words that you can add, for example:

tadi guru menggunakan… – earlier, the teacher used…
sekarang guru menggunakan… – now, the teacher is using…
biasanya guru menggunakan… – usually, the teacher uses…

In your sentence, without extra context, English learners often translate it as a general or habitual present: the teacher uses a mixture of Indonesian and English…

What does menggunakan mean, and how is it different from memakai or pakai?

All three relate to using something, but the nuance and formality differ:

menggunakan
- meaning: to use / to employ
- more formal, common in writing or careful speech
- fits well in your sentence: guru menggunakan campuran…
memakai
- meaning: to use / to wear
- neutral, common in everyday speech
- e.g. guru memakai campuran bahasa Indonesia dan Inggris
pakai (base form, often used without me-)
- meaning: use
- more informal/colloquial
- e.g. gurunya pakai campuran bahasa Indonesia sama bahasa Inggris

All are understandable; menggunakan just sounds more formal and “textbook-like” here.

What exactly does campuran bahasa Indonesia dan Inggris mean? Why is there no dari (of/from)?

campuran is a noun meaning mixture / mix.

So campuran bahasa Indonesia dan Inggris literally means:

a mixture (of) Indonesian and English

In Indonesian, when you say campuran X dan Y, you don’t need a preposition like dari:

campuran gula dan garam – a mixture of sugar and salt
campuran bahasa Indonesia dan Inggris – a mixture of Indonesian and English

The structure is:

campuran + [things being mixed]

You could expand it a bit to:

campuran antara bahasa Indonesia dan bahasa Inggris – also correct, slightly more explicit, but not necessary.

Why is it written bahasa Indonesia and Inggris? What are the capitalization rules?

The usual style is:

bahasa Indonesia
- bahasa (language) is lowercase
- Indonesia (name of the country/language) is capitalized
Inggris (English) is capitalized because it’s a proper name (like “England”).

General rule:

Names of languages / peoples / countries: capitalized
- Indonesia, Inggris, Jepang, Jerman, Arab
The common noun bahasa is not:
- bahasa Indonesia, bahasa Inggris, bahasa Jepang

So your sentence correctly writes bahasa Indonesia and Inggris.

What’s the difference between ketika, saat, and waktu for “when”?

All three can often be translated as when, but they have slightly different flavors:

ketika
- fairly neutral, common in writing and speech
- works well in your sentence: ketika menjelaskan konsep yang sulit
saat
- also neutral, maybe slightly more colloquial than ketika, but still standard
- you can say: …saat menjelaskan konsep yang sulit
waktu
- literally time, but also used as when
- in the “when” sense it sounds a bit more casual in many contexts
- e.g. …waktu menjelaskan konsep yang sulit

In this sentence, all three are grammatically possible; ketika is a good, standard choice, especially in written or semi-formal Indonesian.

In ketika menjelaskan konsep yang sulit, who is doing the explaining, and why is there no subject like guru?

The implied subject is still guru (the teacher) from the previous clause.

Full, explicit version:

…guru menggunakan campuran bahasa Indonesia dan Inggris ketika guru menjelaskan konsep yang sulit.

But Indonesian often drops repeated subjects when it’s clear from context. So it becomes:

…guru menggunakan campuran bahasa Indonesia dan Inggris ketika menjelaskan konsep yang sulit.

Because the clause ketika menjelaskan… is attached to a sentence whose subject is guru, listeners/readers naturally understand that guru is the one explaining the difficult concepts.

You can keep or drop guru after ketika:

ketika guru menjelaskan… – explicit, also correct
ketika menjelaskan… – more concise, also natural

What does yang do in konsep yang sulit? Could we just say konsep sulit instead?

yang introduces a descriptive/relative clause that modifies a noun.

konsep yang sulit = concepts that are difficult / the difficult concepts
- literally: concepts which are difficult

You can say konsep sulit; the difference is subtle:

konsep sulit
- more like difficult concepts as a general description
- sounds a bit more compact and adjective‑like
konsep yang sulit
- slightly more focused or specific: the concepts that are difficult
- can sound a bit more careful or emphasized

In many everyday contexts, they are interchangeable, but konsep yang sulit feels a bit more explicit and is very natural in this sentence.

Why is there a semicolon (;) between the two parts? Could we use a comma or a period instead?

The semicolon separates two closely related independent clauses:

Beberapa pelajar SMA datang ke kelas ini;
guru menggunakan campuran bahasa Indonesia dan Inggris ketika menjelaskan konsep yang sulit.

In Indonesian, as in English, you have several options:

Semicolon (;) – as written; stylistically fine, shows a close connection.
Period (.)
- Beberapa pelajar SMA datang ke kelas ini. Guru menggunakan campuran…
- More neutral and very common.
Comma + conjunction (e.g. dan)
- Beberapa pelajar SMA datang ke kelas ini, dan guru menggunakan campuran…
- Also correct.

So the semicolon is a stylistic choice; a period or “, dan” would also be acceptable here.