Moj um radi brzo.

• Moj = my
• um = mind, intellect
• radi = works
• brzo = quickly / fast

So the sentence literally means My mind works quickly, often translated more naturally as My mind works fast.

Because moj has to match the noun um.

• um is a masculine singular noun
• so the possessive pronoun must also be masculine singular nominative: moj

Compare:

• moj um = my mind (masculine)
• moja knjiga = my book (feminine)
• moje dete = my child (neuter)

It is in the nominative case because it is the subject of the sentence — the thing doing the action.

In Moj um radi brzo, the subject is my mind, so um stays in nominative:

• um = nominative singular

Radi is the 3rd person singular present tense of raditi (to work).

Since the subject is um (mind), which is he/it grammatically singular, Serbian uses:

• ja radim = I work
• ti radiš = you work
• on/ona/ono radi = he/she/it works

So:

• um radi = the mind works

Because brzo is an adverb, while brz is an adjective.

• brz = fast as an adjective, used with a noun
  
  • brz auto would mean a fast car (though normally brz automobil)
• brzo = fast / quickly as an adverb, used with a verb
  
  • radi brzo = works fast

Here, brzo describes how the mind works, so the adverb is needed.

Yes. Serbian word order is fairly flexible.

These are all possible:

• Moj um radi brzo.
• Moj um brzo radi.
• Brzo radi moj um.

The most neutral version is Moj um radi brzo.
Changing the order usually changes emphasis, not the basic meaning.

For example:

• Moj um brzo radi puts brzo a bit closer to the verb
• Brzo radi moj um emphasizes brzo

Yes, sometimes.

You can say:

• Um radi brzo. = The mind works fast / My mind works fast in the right context

But moj makes it clearly my mind and can add emphasis or personal focus.

In Serbian, possessives are often omitted when the meaning is obvious, but keeping them is completely normal.

It is a correct and normal word, but it can sound a bit more intellectual or abstract than English mind in some contexts.

Some related words:

• um = mind, intellect
• mozak = brain
• misli = thoughts

So:

• Moj um radi brzo focuses on the mind/intellect
• Moj mozak radi brzo would sound more like My brain works fast

Both can be understood, but um is more about mental capacity or intellect.

No. Raditi is broader than just to have a job.

It can mean:

• to work physically or mentally
• to function
• to operate

Examples:

• On radi u školi. = He works at a school.
• Sat radi. = The clock works.
• Moj um radi brzo. = My mind works fast.

So here it means functions / operates quickly.

They would probably understand it as something like:

• My mind works fast
• I think quickly
• I process things quickly

It sounds understandable and correct. Depending on context, a Serbian speaker might also say something more idiomatic, such as:

• Brzo razmišljam. = I think quickly
• Moj mozak brzo radi. = My brain works fast

But Moj um radi brzo is still grammatical and clear.

A simple pronunciation guide:

• Moj ≈ moy
• um ≈ oom
• radi ≈ RAH-dee
• brzo ≈ BUR-zoh or BR-zoh depending on how comfortably you pronounce the consonant cluster

So the whole sentence is roughly:

moy oom RAH-dee BUR-zoh

The r in Serbian is rolled or tapped, not the English r.