Learn Hardcore Korean: jeoneun gongwoneseo samsip bun dongan undonghaeyo. - I exercise in the park for thirty minutes.

저 means “I” (humble). The particle -는 is a topic marker, indicating that “I” is the topic of the sentence. In contrast, -가 is a subject marker that often emphasizes the subject or introduces new information. Since you’re talking about what you do (not emphasizing or contrasting “I”), 저는 is more natural here.

Why is 공원에서 using -에서 rather than -에?

The particle -에서 indicates the location where an action takes place (“at/in the park”). If you used -에, it would usually imply destination (“to the park”) or static existence (“in the park”), but not specifically “doing something at that place.” Since 운동해요 (to exercise) is an action occurring in the park, -에서 is required.

What does 삼십 분 동안 mean? Could I just say 삼십 분?

삼십 분 means “thirty minutes,” simply a measure of time. 동안 means “during” or “for [a duration].” Together, 삼십 분 동안 means “for thirty minutes.” Without 동안, you’d just be stating the time span, not explicitly “for” that duration.

Why is it 삼십 (sino-Korean) instead of 서른 (native Korean)?

Both 삼십 and 서른 mean “thirty.” 삼십 is Sino-Korean (used in formal counting, times, price, age in certain contexts), while 서른 is native Korean (often used for counting age or loose quantities). In duration expressions like 삼십 분 동안, both are acceptable, but Sino-Korean numbers are very common for minutes and hours.

What does 운동해요 mean, and why is 해요 instead of 한다 or 해?

운동하다 means “to exercise.” 해요 is the polite present tense ending of the standard speech level (해요체)—used in everyday polite conversation. 한다 is the plain or written style, and 해 is the casual/informal style you might use with close friends or family.

Why is the word order (Topic) (Location) (Duration) (Verb)? Can I rearrange them?

Korean generally follows Subject–Object–Verb order, and modifiers (like time and place) come before the verb. The usual sequence is: Topic → Time → Place → Object → Verb. You can swap time and place (e.g., 삼십 분 동안 공원에서 운동해요), but the verb almost always stays at the end. Changing the order too much can sound awkward.

Can I omit 저는 and just say 공원에서 삼십 분 동안 운동해요?

Yes. Korean often drops the topic or subject when it’s understood from context. If it’s clear you’re talking about yourself, you can start with 공원에서… without any problem.

How would I make this sentence more formal or more casual?

More formal (존댓말, formal written or very polite speech):
저는 공원에서 삼십 분 동안 운동합니다.
More casual (반말, with close friends):
나 공원에서 30분 동안 운동해.
Note changes: dropping the topic marker, using the native number or digit “30,” and using the casual verb ending.