Bạn tớ suy luận rồi bẻ khóa.

Bạn tớ means my friend.

• bạn = friend
• tớ = I / me, used in a casual, friendly way

So bạn tớ is a very common informal way to say my friend.

A slightly fuller version is bạn của tớ, but in everyday speech Vietnamese often drops của in phrases like this.

Both can mean my friend, but the tone is different.

• tớ is casual, friendly, and often used among peers
• tôi is more neutral, formal, or distant

So bạn tớ sounds more natural in relaxed conversation, especially among younger speakers or friends.
If you say bạn tôi, it is still correct, but it may sound more formal depending on context.

Yes, suy luận is a verb here.

It means something like:

• to reason
• to infer
• to deduce

In this sentence, it describes what the friend did first: they used reasoning or deduction.

It can also appear in contexts closer to logical inference or reasoning things out.

Literally, bẻ khóa is something like break the lock or break the code.

In natural English, depending on context, it can mean:

• to crack a lock
• to crack a code
• to unlock something by force or technique
• sometimes even to hack / bypass protection

So the exact English wording depends on what is being opened or broken into in the larger context.

Here, rồi links two actions and shows sequence:

suy luận rồi bẻ khóa
= reasoned it out and then cracked/unlocked it

In this position, rồi often means:

• then
• and then
• after that

It helps show that one action happened before the next one.

So the structure is:

• subject: Bạn tớ
• action 1: suy luận
• linking/sequencing word: rồi
• action 2: bẻ khóa

Related, but not exactly the same use.

Vietnamese rồi has several common uses. Two important ones are:

1. After a verb or between actions: shows completion or sequence

   • ăn rồi = have eaten / ate already
   • suy luận rồi bẻ khóa = reasoned it out and then cracked it

2. At the end of a sentence: often marks a new state or completion

   • Xong rồi. = It’s done already.
   • Muộn rồi. = It’s late already.

So in your sentence, rồi is mainly functioning as a marker of sequence between two actions.

Yes, that is very normal.

Vietnamese often places multiple verbs in one clause when the same subject performs a sequence of actions.

Here:

Bạn tớ suy luận rồi bẻ khóa.

The subject bạn tớ does both actions:

1. suy luận
2. bẻ khóa

English often needs and, then, or a more explicit structure. Vietnamese can do this very compactly.

Vietnamese often omits objects when they are already understood from context.

For example, if everyone already knows what is being analyzed or unlocked, the speaker may simply say:

Bạn tớ suy luận rồi bẻ khóa.

Even though English often prefers something explicit like:

• My friend reasoned it out and cracked the code
• My friend deduced it and unlocked it

Vietnamese is comfortable leaving that unstated if it is obvious in the conversation.

Not directly through verb endings, because Vietnamese verbs do not conjugate for tense the way English verbs do.

The sentence can be understood as past because of context and because rồi suggests completed/sequential actions.

Vietnamese usually relies on:

• context
• time words
• particles like đã, đang, sẽ, rồi

If you wanted to make the past even clearer, you could say:

Bạn tớ đã suy luận rồi bẻ khóa.

But the original sentence can already sound past/completed in the right context.

It is understandable, but whether it sounds fully natural depends on context.

The main thing is that bẻ khóa usually makes listeners expect an object or a clear context, such as:

• a lock
• a code
• a phone
• a protected file/system

So by itself, the sentence can feel a little context-dependent. It works best when the listener already knows what was cracked or unlocked.

For example, in context it could be perfectly natural:

• someone was stuck on a puzzle or locked device
• your friend figured it out and opened it

Without context, some speakers might expect a more explicit sentence.

Yes, you could, but bạn tớ is more natural in everyday speech.

Compare:

• bạn tớ = casual, concise, very common
• bạn của tớ = also correct, a bit fuller, sometimes slightly more explicit

Vietnamese often drops của in possessive phrases when the meaning is clear.

The tones matter here:

• tớ has the sắc tone: rising
• khóa also has the sắc tone: rising

A rough learner-friendly guide:

• tớ sounds a bit like tuh with a short vowel and a rising tone
• khóa sounds roughly like khwah with a rising tone

Also:

• bẻ has the hỏi tone, which dips and rises in Northern Vietnamese
• suy luận has no special linking word in pronunciation; just say it smoothly as two words

If you are learning a Northern accent, tone shape will be especially important for these words.

Yes. Vietnamese has several ways to show sequence. For example:

• Bạn tớ suy luận xong rồi bẻ khóa.
  = My friend finished reasoning it out, then cracked it.

• Bạn tớ suy luận ra rồi bẻ khóa.
  = My friend figured it out and then cracked/unlocked it.

• Sau khi suy luận, bạn tớ bẻ khóa.
  = After reasoning it out, my friend cracked/unlocked it.

Your original sentence is compact and natural in the right context, but these versions can make the timeline or meaning more explicit.